We report on the reduction of contact resistance in solution-processed TIPS-pentacene (6,13-bis(triisopropylsilylethynyl)pentacene) and PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) top-gate bottom-contact organic field-effect transistors (OFETs) by using different contact-modification strategies. The study compares the contact resistance values in devices that comprise Au source/drain electrodes either treated with 2,3,4,5,6-pentafluorothiophenol (PFBT), or modified with an evaporated thin layer of the metal–organic molecular dopant molybdenum tris-[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd)3), or modified with a thin layer of the oxide MoO3. An improved performance is observed in devices modified with Mo(tfd)3 or MoO3 as compared to devices in which Au electrodes are modified with PFBT. We discuss the origin of the decrease in contact resistance in terms of increase of the work function of the modified Au electrodes, Fermi-level pinning effects, and decrease of bulk resistance by electrically doping the organic semiconductor films in the vicinity of the source/drain electrodes.Keywords: contact doping; contact resistance; Fermi-level pinning; molybdenum trioxide; molybdenum tris-[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene]; organic field-effect transistors; TIPS-pentacene/PTAA; top-gate geometry

•A transparent SU8 photopatternable polymer is used as a flexible substrate.•Electroplated thick metal grids are embedded in a flexible substrate.•Embedded thick metal grids allow uniform spin coating of organic semiconductor layers.•The FF and VOC are comparable to values reported on small-area solar cells.We report on ITO-free large-area flexible organic solar cells with embedded thick metal grids. Embedded thick metal grids on flexible substrates allow uniform spin coating of thin layers of PEDOT:PSS (PH1000) semitransparent electrodes and organic semiconductor layers. A transparent SU8 photo-patternable polymer is used as a flexible substrate. Electroplated copper metallic grids, up to 15 μm thick, defined by photolithography, produce a shadow area of 5.5% of the active area. Inverted solar cells with an active area of 9.3 ± 0.2 cm2, exhibited a fill factor of 0.53 ± 0.06, and an open-circuit voltage of 808 ± 5 mV and a short-circuit current density of 5.5 ± 0.5 mA/cm2, yielding a power conversion efficiency of 2.4 ± 0.4% under 100 mW/cm2 air mass 1.5G illumination. The fill-factor and open circuit voltage values of large-area solar cells are comparable to values reported on small-area solar cells.Embedded thick metal grids on flexible substrates allow uniform spin coating of thin layers of PEDOT:PSS (PH1000) semitransparent electrodes and organic semiconductor layers. Inverted solar cells with an active area of 9.3 ± 0.2 cm2, exhibited a fill factor of 0.53 ± 0.06, and an open-circuit voltage of 808 ± 5 mV and a short-circuit current density of 5.5 ± 0.5 mA/cm2, yielding a power conversion efficiency of 2.4 ± 0.4% under 100 mW/cm2 AM 1.5G illumination.

We report on semitransparent air-processed all-plastic solar cells, fabricated from vacuum-free processes, comprising two polymer electrodes, a polymeric work-function modification layer and a polymer:fullerene photoactive layer. The active layer and the top PEDOT:PSS electrode were prepared by sequential film-transfer lamination on polyethylenimine-modified PEDOT:PSS bottom electrodes. The transferring of films offers ease of layer patterning and the misalignment of defects in the different layers resulting from the additive film transfer lamination process yields high shunt resistance values of 108 ohm cm2. Consequently, all-plastic solar cells fabricated with this process exhibit very low reverse bias dark current and can operate in the photovoltaic quadrant with light irradiance varying over five orders of magnitude. The analysis of the values of the open-circuit voltage as a function of light irradiance over that wide dynamic range points toward an ideality factor of n = 1.82 and a reverse saturation current density of 6.2 × 10−11 A cm−2 for solar cells with an active layer comprised of a blend of poly(3-hexylthiophene) and an indene fullerene bis-adduct.

The use of organic field-effect transistors (OFETs) as sensors in aqueous media has gained increased attention for environmental monitoring and medical diagnostics. However, stable operation of OFETs in aqueous media is particularly challenging because of electrolytic hydrolysis of water, high ionic conduction through the analyte, and irreversible damage of organic semiconductors when exposed to water. To date, OFET sensors have shown the capability of label-free sensing of various chemical/biological species, but they could only be used once because their operational stability and lifetime while operating in aqueous environments has been poor, and their response times typically slow. Here, we report on OFETs with unprecedented water stability. These OFETs are suitable for the implementation of reusable chemical/biological sensors because they primarily respond to charged species diluted in an aqueous media by rapidly shifting their threshold voltage. These OFET sensors present stable current baselines and saturated signals which are ideal for detection of low concentration of small or large molecules that alter the pH of an aqueous environment. The overall response of these OFET sensors paves the way for the development of continuous chemical/biological nondestructive sensor applications in aqueous media.Keywords: fast chemical detection; organic field-effect transistor; reusability; water-stability;

We report on a systematic investigation on the performance and stability of p-channel and n-channel top-gate OFETs, with a CYTOP/Al2O3 bilayer gate dielectric, exposed to controlled dry oxygen and humid atmospheres. Despite the severe conditions of environmental exposure, p-channel and n-channel top-gate OFETs show only minor changes of their performance parameters without undergoing irreversible damage. When correlated with the conditions of environmental exposure, these changes provide new insight into the possible physical mechanisms in the presence of oxygen and water. Photoexcited charge collection spectroscopy experiments provided further evidence of oxygen and water effects on OFETs. Top-gate OFETs also display outstanding durability, even when exposed to oxygen plasma and subsequent immersion in water or operated under aqueous media. These remarkable properties arise as a consequence of the use of relatively air stable organic semiconductors and proper engineering of the OFET structure.Keywords: CYTOP/Al2O3 bilayer dielectric; device reliability; organic electronics; organic field-effect transistors; photoexcited charge collection spectroscopy; soluble organic semiconductor;

Efficient organic photovoltaic cells (OPV) often contain highly reactive low-work-function calcium electron-collecting electrodes. In this work, efficient OPV are demonstrated in which calcium electrodes were avoided by depositing a thin layer of the amine-containing nonconjugated polymer, polyethylenimine (PEIE), between the photoactive organic semiconductor layer and stable metal electrodes such as aluminum, silver, or gold. Devices with structure ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/poly(3-hexylthiophene):indene-C60-bis-adduct (P3HT:ICBA)/PEIE/Al demonstrated overall photovoltaic device performance comparable to devices containing calcium electron-collecting electrodes, ITO/PEDOT:PSS/P3HT:ICBA/Ca/Al, with open-circuit voltage of 775 ± 6 mV, short-circuit current density of 9.1 ± 0.5 mA cm–2, fill factor of 0.65 ± 0.01, and power conversion efficiency of 4.6 ± 0.3%, averaged over 5 devices at 1 sun.Keywords: interlayers; low-work-function electrodes; polyethylenimine; polymer solar cells; water-/alcohol-soluble polymers;

•A via-hole patterning method by reverse stamping for printed organic electronics has been proposed.•The structural and electrical analysis of the via-holes has been performed.•Simple circuits including ring oscillators and decoders have been fabricated and demonstrated using the method.We report on a reverse stamping method to produce via-holes in circuits comprising acene-based top-gate organic field-effect transistors (OFETs) having a CYTOP/Al2O3 (by atomic layer deposition) bilayer gate dielectric. This method relies on the weak adhesive force that exists between a small molecule acene film and a polymer to enable easy delamination of the bilayer gate dielectric by using a PDMS stamp. We demonstrate the effectiveness of this method by fabricating simple circuits using top-gate triisopropylsilylethynyl pentacene (TIPS-pentacene)/poly (triarylamine) (PTAA) OFETs.

•Recyclable solar cells on cellulose nanocrystal substrates are fabricated.•Conducting polymer top electrode is prepared by film-transfer lamination.•The dry process of top electrode avoids swelling damage to the cellulose substrate.•Solar cells exhibit a power conversion efficiency of 4.0%.We report on efficient solar cells on recyclable cellulose nanocrystal (CNC) substrates with a new device structure wherein polyethylenimine-modified Ag is used as the bottom electron-collecting electrode and high-conductivity poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS, PH1000) is used as the semitransparent top hole-collecting electrode. The PEDOT:PSS top electrode is deposited by a film-transfer lamination technique. This dry process avoids swelling damage to the CNC substrate, which is observed when PEDOT:PSS is directly spin-coated from an aqueous solution. Solar cells on recyclable CNC substrates exhibit a maximum power conversion efficiency of 4.0% with a large fill factor of 0.64 ± 0.02 when illuminated through the top semitransparent PEDOT:PSS electrode. The performance of solar cells on CNC substrates is comparable to that of reference solar cells on polyethersulfone substrates.Graphical abstract

•Fluorine-doped tin oxide (FTO) is modified by polyethylenimine ethoxylated.•Inverted organic solar cells are fabricated with the modified FTO.•The solar cells exhibit a power conversion efficiency of 6.3%.•Ultraviolet (UV) illumination reduces work function of FTO from 4.66 to 4.34 eV.•UV illumination induces desorption of oxygen trapped in FTO.We report on inverted solar cells using amine-containing polymer (polyethylenimine ethoxylated, PEIE) modified fluorine-doped tin oxide (FTO) as the electron-collecting electrode. PEIE lowers the work function of FTO from 4.6 eV to 3.8 eV, measured by Kelvin probe, sufficiently low for collecting electrons in solar cells. With the FTO/PEIE electrode, inverted solar cells based on poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl]:phenyl-C61-butyric acid methyl ester exhibited an open-circuit voltage of 0.70 ± 0.01 V, a short-circuit current density of 15.2 ± 0.2 mA/cm2, a fill factor of 0.60 ± 0.01 and a power conversion efficiency of 6.3 ± 0.2% averaged over 9 devices under 100 mW/cm2 AM1.5 illumination, which is comparable to the solar cells fabricated on indium–tin oxide glass substrates. In addition, we found that ultraviolet light-containing illumination can reduce the work function of bare FTO from 4.66 eV to 4.34 eV presumably because of the desorption of oxygen trapped in FTO.

Green electrophosphorescent inverted top-emitting organic light-emitting diodes with a Ag/1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) anode are demonstrated. A high current efficacy of 124.7 cd/A is achieved at a luminance of 100 cd/m2 when an optical outcoupling layer of N,N′-di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl-4,4′-diamine (α-NPD) is deposited on the anode. The devices have a low turn-on voltage of 3.0 V and exhibit low current efficacy roll-off through luminance values up to 10,000 cd/m2. The angle dependent spectra show deviation from Lambertian emission and color change with viewing angle. Hole-dominated devices with Ag/HAT-CN electrodes show current densities up to three orders of magnitude higher than devices without HAT-CN.Graphical abstractHighlights► Green electrophosphorescent inverted top-emitting OLEDs with a Ag/HAT-CN anode. ► Current efficacy of 124.7 cd/A at luminance of 100 cd/m2 with optical outcoupling. ► Low turn-on of 3.0 V and low current efficacy roll-off through 10,000 cd/m2. ► Hole-dominated devices with Ag/HAT-CN show higher current than devices with just Ag.

•Polymer solar cells with a NiO hole-collecting interlayer are demonstrated.•NiO is deposited by atomic layer deposition.•O2-plasma treatment on NiO films improves device performance.•The polymer solar cells with P3HT:IC60BA yield an efficiency of 4.1 ± 0.2%.We report on the photovoltaic properties of polymer solar cells that use NiO-coated indium tin oxide (ITO) as the hole-collecting electrode. The NiO films were prepared by atomic layer deposition (ALD) on top of ITO with thicknesses varying from 6 to 25 nm. The NiO films increase the work function (WF) of the ITO, allowing NiO-coated ITO to act as an efficient hole-collecting electrode. Devices made with pristine NiO showed poor current–voltage characteristics. However, subsequent O2-plasma treatment further increased the WF of NiO, tuning NiO-coated ITO into an efficient hole-collecting electrode for polymer solar cells based on the donor poly(3-hexylthiophene-2,5-diyl) (P3HT). The polymer solar cells with the O2-plasma treated NiO-coated ITO hole-collecting electrodes yield a power conversion efficiency of 4.1 ± 0.2% under simulated air mass 1.5 G 100 mW/cm2 illumination, which is comparable to reference devices with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)-coated ITO hole-collecting electrodes.Graphical abstract

We report on inverted polymer tandem solar cells wherein the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), modified at one interface with ethoxylated polyethylenimine (PEIE), acts as an efficient charge recombination layer. This recombination layer shows very low optical absorption, high electrical conductivity, and a large work function contrast of 1.3 eV between its top and bottom interfaces. Its use yields tandem cells in which the open-circuit voltage is the sum of that of individual cells. The fill factor of tandem cells connected in series is found to be larger than that of single-junction cells. Its simple polymeric composition and its unprecedented performance make it a promising component for emerging organic photovoltaic technologies.

We report on a systematic study of solvent and polymer matrix effects on the phase segregation behavior of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) blends incorporated into two different amorphous polymer matrices, poly (α-methyl styrene) and poly (triarylamine), and using two solvents, chlorobenzene and tetralin. Optical microscopy, X-ray diffraction analyses, and optical absorption measurements are used to evaluate the film morphology, crystallinity, and optical density, respectively. These analyses are correlated with the extent of vertical segregation of TIPS-pentacene, as observed for the blended films by depth-profile XPS analyses. The microstructure and vertical phase segregation of TIPS-pentacene in blend films are found to be strongly influenced by the choice of solvent. Tetralin, a solvent with a high boiling temperature, was found to be more desirable for achieving distinct phase segregation/crystallization of TIPS-pentacene in blend films and best performance in OFETs with a dual-gate geometry. The electrical properties of top and bottom channels were consistent with the morphological characterization and OFETs processed from tetralin showed higher mobility values than those from chlorobenzene. Further modification of the annealing conditions in the TIPS-pentacene/PTAA/tetralin ternary system led to top-gate OFETs with mobility values up to 2.82 cm2/Vs.

We report on reversible changes of the work function (WF) values of indium-tin-oxide (ITO) under prolonged ultraviolet (UV) and air exposure. The WF of ITO is reduced from 4.7 eV to 4.2 eV by photon absorption in ITO under UV illumination or an air mass 1.5 solar simulator (100 mW cm−2). Air or oxygen exposure is found to increase the WF of ITO (UV-exposed) to a value of 4.6 eV. These changes of ITO's WF lead to reversible variations of the performance of organic photovoltaic devices where ITO acts primarily as the electron collecting or hole collecting electrode. These variations can be reflected in the disappearance (or appearance) of an S-shaped kink in the J–V characteristics upon continuous UV or solar simulator illumination (or air exposure). This reversible phenomenon is ascribed to the adsorption and desorption of oxygen on the surface and grain boundaries of ITO. The use of surface modifiers to either decrease or increase the WF of ITO in organic photovoltaic devices with inverted and conventional geometries is also shown to be an effective route to stabilize the device performance under UV illumination.

Performance of pentacene organic field-effect transistors (OFETs) is significantly improved by treatment of SiO2 with octyltrichlorosilane (OTS-8) compared to octadecyltrichlorosilane (OTS-18). The average hole mobility in these OFETs is increased from 0.4 to 0.8 cm2/Vs when treating the dielectric with OTS-8 versus OTS-18 treated devices. The atomic force microscope (AFM) images show that the OTS-8 treated surface produces much larger grains of pentacene (∼500 nm) compared to OTS-18 (∼100 nm). X-ray diffraction (XRD) results confirmed that the pentacene on OTS-8 is more crystalline compared to the pentacene on OTS-18, resulting in higher hole mobility.Graphical abstractHighlights► Comparison of pentacene OFETs upon SiO2 modification with OTS-8 and OTS-18. ► Larger grains and higher degree of crystallinity observed with pentacene on OTS-8. ► Field-effect mobility improved from 0.4 cm2/Vs for OTS-18 to 0.8 cm2/Vs for OTS-8. ► Mobility increase due to larger grain sizes and higher crystallinity in pentacene.

We report on high-mobility top-gate organic field-effect transistors (OFETs) and complementary-like inverters fabricated with a solution-processed molecular bis(naphthalene diimide)-dithienopyrrole derivative as the channel semiconductor and a CYTOP/Al2O3 bilayer as the gate dielectric. The OFETs showed ambipolar behavior with average electron and hole mobility values of 1.2 and 0.01 cm2 V−1 s−1, respectively. Complementary-like inverters fabricated with two ambipolar OFETs showed hysteresis-free voltage transfer characteristics with negligible variations of switching threshold voltages and yielded very high DC gain values of more than 90 V/V (up to 122 V/V) at a supply voltage of 25 V.Graphical abstractHighlights► Top-gate bottom-contact OFETs with ambipolar semiconductor were characterized. ► Average electron mobility value of 1.2 cm2 V−1 s−1 was obtained. ► Average hole mobility value of 0.01 cm2 V−1 s−1 was obtained. ► Complementary-like inverters had hysteresis-free voltage transfer characteristics. ► Inverters had high DC gain values of up to 122 V/V.

The effect of the macromolecular additive, polydimethylsiloxane (PDMS), on the performance of solution processed molecular bulk heterojunction solar cells is investigated, and the addition of PDMS is shown to improve device power conversion efficiency by ∼70% and significantly reduce cell-to-cell variation, from a power conversion efficiency of 1.25 ± 0.37% with no PDMS to 2.16 ± 0.09% upon the addition of 0.1 mg/mL PDMS to the casting solution. The cells are based on a thiophene and isoindigo containing oligomer as the electron donor and [6,6]-phenyl-C61 butyric acid methyl ester (PC61BM) as the electron acceptor. PDMS is shown to have a strong influence on film morphology, with a significant decrease in film roughness and feature size observed. The morphology change leads to improved performance parameters, most notably an increase in the short circuit current density from 4.3 to 6.8 mA/cm2 upon addition of 0.1 mg/mL PDMS. The use of PDMS is of particular interest, as this additive appears frequently as a lubricant in plastic syringes commonly used in device fabrication; therefore, PDMS may unintentionally be incorporated into device active layers.Keywords: additive processing; bulk heterojunction; molecular photovoltaic cell; morphology control; organic solar cell

Highly stable, solution-processed, small molecule-polymer blend organic field-effect transistors (OFETs) with a top-gate geometry were demonstrated on a flexible polyethersulfone (PES) substrate. The top-gate dielectric was a bi-layer comprised of CYTOP and a high-k Al2O3 layer grown by atomic layer deposition (ALD). A solution processed 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and poly(triarylamine) (PTAA) blend was used as the organic semiconductor. TIPS-pentacene and PTAA blend OFETs with the CYTOP/Al2O3 bi-layer top gate dielectric showed an averaged saturation mobility value of 0.24 ± 0.08 cm2/Vs at operation voltages below 8 V. A constant direct-current bias stress test was carried out to examine their operational stability for 2 h. Under bias stress, neither significant change in mobility nor shift in the threshold voltage has been observed in these OFETs. To evaluate the real potential of these OFETs towards the development of circuit components commonly used in electronic applications, a resistive-load inverter was implemented by connecting an OFET to an external load resistor. Excellent stability of the transistor led to electrically stable inverters with negligible variations of the voltage transfer characteristics before and after bias stress. After the operational stability test, these OFETs were exposed to air and then were subjected to bending experiments. Even after exposure to air for 4 months and bending for 30 min, no significant changes in performance were observed in either a single transistor device or in a resistive-load inverter.Graphical abstractHighly stable, solution-processed, small molecule-polymer blend organic field-effect transistors with a top-gate geometry were demonstrated on a flexible polyethersulfone substrate. Excellent stability of the transistor led to stable resistive-load inverter with negligible variations of the voltage transfer characteristics after bias stress, air exposure, and mechanical deformation.Highlights► Flexible, stable and solution-processed organic transistors with bi-layer gate dielectric. ► Environmental and mechanical stability of organic transistors on flexible substrates. ► Stable resistive-load inverters on flexible substrate fabricated from transistors. ► Negligible variations of the inverter behaviors after various test conditions.

We report on vertically stacked complementary inverters implemented with a solution-processed [6,6]-phenyl c61 butyric acid methyl ester (PCBM) n-channel thin-film transistor (TFT) fabricated on top of a 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and poly(triarylamine) (PTAA) blend p-channel TFT. With a shared common gate electrode positioned between two dielectric layers, bottom-contact p- and top-contact n-channel TFTs showed saturation mobility values of 0.25 and 0.004 cm2/V s and threshold voltages of −3.9, and 0.3 V, respectively. The inverter yielded a gain value of −24 V/V with a switching threshold voltage value of 3.3 V at a supply voltage of 7 V. This demonstration of the use of solution-processed semiconductors in a vertically stacked complementary inverter geometry is a step forward towards the development of low-cost complementary electronics.Graphical abstractHighlights► Solution-processed p- and n-channel organic semiconductors. ► Vertically stacked p- and n-channel transistors and complementary inverters. ► Independent control of capacitance density and gate dielectric interfaces. ► Low temperature processing below 110 °C. ► High packing density and interconnectivity.

We report on semitransparent organic solar cells using a single-layer blend based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the top electrode. The PEDOT:PSS blend was prepared by mixing a high-conductivity formulation of PEDOT:PSS (H.C. Starck CLEVIOS PH-1000) and another formulation of PEDOT:PSS (H.C. Starck CLEVIOS CPP 105D). The PEDOT:PSS blend yields good wetting properties on the hydrophobic surface of a blend of poly(3-hexylthiophene) (P3HT) with phenyl-C61-butyric acid methyl ester (PC60BM), and shows a conductivity over 400 S cm−1. Semitransparent organic solar cells using the PEDOT:PSS blend as the top electrode with a structure of glass/ITO/ZnO/P3HT:PC60BM/PEDOT:PSS-blend exhibited an average power conversion efficiency of 2.4% estimated for 100 mW cm−2 AM 1.5G illumination.Graphical abstractResearch highlights► Semitransparent organic solar cells were demonstrated with a PEDOT:PSS blend as the top electrode fabricated by one-step spin-coating processing. ► The PEDOT:PSS blend yielded a high conductivity of 420 S cm-1 and its solution showed good wetting properties on the hydrophobic surface of an organic active layer. ► The power conversion efficiency of the semitransparent solar cells reached 2.4% estimated for 100 mW cm-2 AM 1.5G illumination.

High-efficiency organic light-emitting devices (OLEDs) were fabricated in which solution-processed ambipolar blends of hole- and electron-transport polymer hosts doped with a green-emitting iridium complex are sandwiched between a photocrosslinked hole-transporting layer and a vacuum-deposited electron-transporting layer. The ambipolar host blends consist of blends of bis-oxadiazole-functionalized poly(norbornene) electron-transport materials and poly(N-vinylcarbazole). For the best device examined, an external quantum efficiency of 13.6% and a maximum luminous efficiency of 44.6 cd/A at 1000 cd/m2 with a turn-on voltage of 5.9 V were obtained.Graphical abstractCurrent density–voltage characteristics, luminance and external quantum efficiency as a function of applied voltage of an OLED device based on side-chain polymer blends. Inset: device architecture.Research highlights► Efficient organic light-emitting diodes with an emissive layer comprised of a blend of side-chain polymers and doped with the phosphor Ir(ppy)3 or Ir(pppy)3. ► Ambipolar emissive layer comprised of poly(N-vinylcarbazole) and one of two bis-oxadiazole side-chain polymers. ► A combination of side-chain polymers with hole and electron transport properties and doped with a green emitting phosphor.

We report on the properties of inverted polymer solar cells using an ultrathin Al2O3 buffer layer on indium tin oxide (ITO). The ultrathin Al2O3 layer, deposited by the atomic layer deposition method, was found to reduce the work function of ITO and turns ITO into an electron-collecting electrode. The current density–voltage characteristics of unexposed devices showed an s-shape kink. The kink was eliminated upon exposure to ultraviolet (UV) illumination. Inverted solar cells based on P3HT:PC60BM yielded a fill factor of 0.64 and a power conversion efficiency of about 2.8% estimated for 100 mW cm−2 simulated AM 1.5 illumination.

A series of highly soluble donor–acceptor (D–A) copolymers containing N-(3,4,5-tri-n-decyloxyphenyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) or N-(2-decyltetradecyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP′) as donor and three different acceptors, 4,7-dithien-2-yl-[2,1,3]-benzothiadiazole, 4,9-dithien-2-yl-6,7-di-n-hexyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 4,8-dithien-2-yl-2λ4δ2-benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole (BThX, X = BTD, TQHx2, BBT, respectively) were synthesized by Stille coupling polymerizations. The optical and electrochemical properties of these copolymers were investigated, along with their use in field-effect transistors and photovoltaic devices. The band gaps (eV) estimated from UV-vis-NIR spectra and electrochemical measurements of the copolymers varied from ca. 1.5–0.5 eV, and were consistent with quantum-chemical estimates extrapolated using density functional theory. Oxidative and reductive spectroelectrochemistry of the copolymers indicated they can be both p-doped and n-doped, and three to four differently colored redox states of the polymers can be accessed through electrochemical oxidation or reduction. The DTP-BThBTD and DTP-BThTQHx2 copolymers exhibited average field-effect hole mobilities of 1.2 × 10−4 and 2.2 × 10−3 cm2/(Vs), respectively. DTP-BThBBT exhibited ambipolar field-effect characteristics and showed hole and electron mobilities of 1.2 × 10−3 and 5.8 × 10−4 cm2/(Vs), respectively. Bulk heterojunction photovoltaic devices made from blends of the copolymers with 3′-phenyl-3′H-cyclopropa[1,9](C60-Ih)[5,6]fullerene-3′-butanoic acid methyl ester (PCBM) (1:3 weight ratio) exhibited average power conversion efficiencies as high as 1.3% under simulated irradiance of 75 mW/cm2.

We report on ambipolar thin-film transistors (ATFTs) that use a co-planar channel geometry to achieve balanced ambipolar operation. Using this geometry, we demonstrate hybrid organic–inorganic high performance ATFTs consisting of amorphous-InGaZnO (mobility of 10 cm2/Vs) and pentacene channels (mobility of 0.3 cm2/Vs) with performance parameters comparable to those of unipolar TFTs fabricated from these same semiconductors. A key characteristic of this co-planar channel ATFT geometry is that the onset of ambipolar operation is mediated by a new operating regime where one of the channels can reach saturation while the other channel remains off. This allows these ATFTs to reach high on–off current ratios approaching 104 at 5 V, close to the saturation regime.

Hybrid organic–inorganic complementary inverters composed of pentacene and amorphous InGaZnO for p- and n-channel thin-film transistors (TFTs) were fabricated on flexible polyethersulfone substrates. The p- and n-channel TFTs showed saturation mobility values of 0.15 and 3.8 cm2/Vs, respectively. We propose a new method to find the switching threshold voltage and the optimum supply voltage of complementary inverters. With this method, we demonstrate hybrid complementary inverters that at a supply voltage of 25 V show a high gain of 130 V/V at a switching threshold voltage of 12.5 V. Operating these inverters at the ideal supply voltage leads to high and balanced noise margins with values of 84% of their theoretical maximum.

The contact resistance in pentacene organic field-effect transistors (OFETs) is found to be significantly reduced by selectively doping the organic semiconductor region beneath the source/drain electrodes. A 10 nm co-evaporated (1:1 ratio) layer of molybdenum tris-[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] and pentacene was deposited under the metal electrodes for this purpose. The width-normalized contact resistance (varying channel lengths of 25–200 μm used for the study) in contact-doped devices was lowered significantly (0.5 kΩ-cm) in comparison to reference devices (3.4 kΩ-cm) in the accumulation regime (VGS = −30 V). Doping of the contacts did not affect the stability of the devices under continuous bias stress significantly.

We report on the photovoltaic properties of inverted polymer solar cells where the transparent electron-collecting electrode is formed by a ZnO-modified indium−tin oxide (ITO) electrode. The ZnO layers were deposited by atomic layer deposition (ALD) with varying thicknesses from 0.1 to 100 nm. The work function, surface roughness, and morphology of ITO/ZnO were found to be independent of the ZnO thickness. However, the device performance was found to be strongly dependent on a critical ZnO thickness, around 10 nm. Below the critical thickness the device performance was degraded because of the appearance of a “kink” in the current−voltage characteristics. The kink features became less pronounced after ultraviolet (UV) exposure. This was attributed to oxygen desorption, leading to an increased conductivity of the ZnO layer. At and above this critical thickness, the device performance significantly improved and no longer depended strongly on the thickness of the ZnO layer, in agreement with optical simulations. Instead, these optical simulations showed that the thickness of the active layer plays a more important role than the thickness of the ZnO layer in optimizing the photovoltaic properties of inverted solar cells. Inverted polymer solar cells with an increased thickness of the active layer showed a power conversion efficiency (PCE) of 3.06% estimated for AM1.5G, a 100 mW cm−2 illumination.

Organic photovoltaics, which convert sunlight into electricity with thin films of organic semiconductors, have been the subject of active research over the past 20 years. The global energy challenge has greatly increased interest in this technology in recent years. Low-temperature processing of organic small molecules from the vapor phase or of polymers from solution can confer organic semiconductors with a critical advantage over inorganic photovoltaic materials since the high-temperature processing requirements of the latter limit the range of substrates on which they can be deposited. Unfortunately, despite significant advances, the power conversion efficiency of organic solar cells remains low, with maximum values in the range of 6%. A better understanding of the physical processes that determine the efficiency of organic photovoltaic cells is crucial to enhancing their competitiveness with other thin-film technologies. Maximum values for the photocurrent can be estimated from the light-harvesting capability of the individual molecules or polymers in the device. However, a better understanding of the materials-level processes, particularly those in layer-to-layer interfaces, that determine the open-circuit voltage (VOC) in organic solar cells is critical and remains the subject of active research. The conventional wisdom is to use organic semiconductors with smaller band gaps to harvest a larger portion of the solar spectrum. This method is not always an effective prescription for increasing efficiency: it ignores the fact that the value of VOC is generally decreased in devices employing materials with smaller band gaps, as is the case with inorganic semiconductors. In this Account, we discuss the influence of the different interfaces formed in organic multilayer photovoltaic devices on the value of VOC; we use pentacene−C60 solar cells as a model. In particular, we use top and bottom electrodes with different work function values, finding that VOC is nearly invariant. In contrast, studies on devices incorporating hole-transport layers with different ionization potentials confirm that the value of VOC depends largely on the relative energy levels of the donor and acceptor species that form the essential heterojunction. An analysis of the properties of solar cells using equivalent-circuit methods reveals that VOC is proportional to the logarithm of the ratio of the photocurrent density Jph divided by the reverse saturation current density J0. Hence, an understanding of the physical origin of J0 directly yields information on what limits VOC. We assign the physical origin of J0 to the thermal excitation of carriers from the donor to the acceptor materials that form the organic heterojunction. Finally, we show that the solution to achieving higher power conversion efficiency in organic solar cells will be to control simultaneously the energetics and the electronic coupling between the donor and acceptor materials, in both the ground and excited state.

We review potential applications of third-harmonic generation (THG) in polymer composites to implement optical image processing applications at the eye-safe and technologically relevant telecommunication bands. We discuss two examples, time-gated imaging through scattering media, and image recognition using Fourier-based techniques, where THG in a polymer composite offers significant advantages over typical holographic media, in that it produces signals that are non-degenerate in optical frequency and space, and allows the development of applications that are compatible with low-cost Si-based electronic components.

Six N,N′,5,11-tetrasubstituted coronene-2,3,8,9-tetracarboxydiimides have been synthesised incorporating 3,4,5-tri(n-dodecyloxy)phenyl or 2-(n-decyl)-n-tetradecyl groups in various positions. Differential scanning calorimetry, polarised optical microscopy, and X-ray diffraction indicate that all form columnar discotic mesophases from around room temperature to around 200 °C. Charge-carrier mobility values, which energetic considerations suggest are electron mobility values, have been determined in non-aligned samples cooled from the isotropic melt using the space-charge-limited current technique. The highest mobility, 6.7 cm2V−1 s−1, was found in N,N′-bis(n-2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecylfluorooctyl)-5,11-bis(3-[{3,4,5-tri(n-dodecyloxy)phenyl}carbonyloxy]-n-propyl)coronene-2,3,8,9-tetracarboxydiimide, which X-ray diffraction suggests is the most highly ordered of the materials examined.

We investigate the effects of surface modification of indium tin oxide (ITO) on the performance of organic multilayer molecular photovoltaic devices based on pentacene/C60 bi-layer heterojunctions. Values of the open-circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (η) are found invariant of the work function and surface hydrophobicity of ITO. Insensitivity of these parameters to variations of work function in the range of 4.50 to 5.40 eV achieved through the use of surface modifiers are correlated with an invariance of the barrier height (∼0.6 eV) due to Fermi level pinning at the ITO/pentacene interface. Energy barrier heights are extracted independently from the analysis of the electrical characteristics of single-layer diodes based on modified ITO and pentacene using an equivalent circuit model.

Low-voltage pentacene organic field-effect transistors (OFETs) with different gate dielectric interfaces are studied and their performance in terms of electrical properties and operational stability is compared. Overall high electrical performance is demonstrated at low voltage by using a 100 nm-thick high-κ gate dielectric layer of aluminum oxide (Al2O3) fabricated by atomic layer deposition (ALD) and modified with hydroxyl-free low-κ polymers like polystyrene (PS), divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) (Cyclotene™, Dow Chemicals), and as well as with the widely used octadecyl-trichlorosilane (OTS). Devices with PS and BCB dielectric surfaces exhibit almost similar electrical performance with high field-effect mobilities, low subthreshold voltages, and high on/off current ratios. The higher mobility in pentacene transistors with PS can be correlated to the better structural ordering of pentacene films, as demonstrated by atomic force microscopy (AFM) images and X-ray diffraction (XRD). The devices with PS show good electrical stability under bias stress conditions (VGS = VDS = −10 V for 1 h), resulting in a negligible drop (∼2%) in saturation current (IDS) in comparison to that in devices with OTS (∼12%), and to a very high decay (∼30%) for the devices with BCB.

A study of the influence of the deposition rate of top-contact Au source and drain electrodes deposited by electron-beam evaporation on the electrical performance of pentacene organic field-effect transistors (OFETs) is presented. By adjusting the deposition rate of the Au electrodes to minimize metal diffusion into the semiconductor pentacene layer, the source/drain contact resistance could be reduced. At a Au deposition rate of 10 Å/s, high-performance pentacene p-channel OFETs were obtained with a field-effect mobility of 0.9 cm2/Vs and a normalized channel width resistance of 23 kΩ cm in a device with a channel length of 25 μm.

The charge-carrier mobilities for three Ni bis(dithiolene) complexes have been determined using the steady-state space-charge limited current technique. A high mobility of 2.8 cm2 V–1 s–1 was observed for one compound, which exhibits a π-stacked columnar structure, in an annealed unsymmetrical melt-processed device. Energy-level considerations and field-effect transistor measurements suggest that this value represents an electron mobility. However, saturation mobilities measured for this compound in spin-coated field-effect transistors were found to be over two orders of magnitude lower than the space-charge limited current values. X-Ray diffraction shows a difference in morphology between thick melt-processed and thin spin-coated films and, therefore, a significant change in intermolecular packing between the device types may explain the discrepancy in mobilities obtained using the two techniques.

High-performance pentacene field-effect transistors have been fabricated using Al2O3 as a gate dielectric material grown by atomic layer deposition (ALD). Hole mobility values of 1.5 ± 0.2 cm2/V s and 0.9 ± 0.1 cm2/V s were obtained when using heavily n-doped silicon (n+-Si) and ITO-coated glass as gate electrodes, respectively. These transistors were operated in enhancement mode with a zero turn-on voltage and exhibited a low threshold voltage (< −10 V) as well as a low sub-threshold slope (<1 V/decade) and an on/off current ratio larger than 106. Atomic force microscopy (AFM) images of pentacene films on Al2O3 treated with octadecyltrichlorosilane (OTS) revealed well-ordered island formation, and X-ray diffraction patterns showed characteristics of a “thin film” phase. Low surface trap density and high capacitance density of Al2O3 gate insulators also contributed to the high performance of pentacene field-effect transistors.

We report on the photovoltaic properties of organic solar cells based on pentacene and C60 thin films with a focus on their spectral responses and the effect of thermal annealing. Spectra of external quantum efficiency (EQE) are measured and analyzed with a one-dimensional exciton diffusion model dependent upon the complex optical functions of pentacene films, which are measured by spectroscopic ellipsometry. An improvement in EQE is observed when the thickness of the bathocuproine (BCP) layer is decreased from 12 nm to 6 nm. Detailed analysis of the EQE spectra indicates that large exciton diffusion lengths in the pentacene films are responsible for the overall high EQE values near wavelengths of 668 nm. Analysis also shows that improvement in the EQE of devices with the thinner BCP layer can be attributed to a net gain in optical field distribution and improvement in carrier collection efficiency. An improvement in open-circuit voltage (VOC) is also achieved through a thermal annealing process, leading to a net increase in power conversion efficiency. Integration of the EQE spectrum with an AM1.5 G spectrum yields a predicted power conversion efficiency of 1.8 ± 0.2%. The increase in VOC is attributed to a significant reduction in the diode reverse saturation current upon annealing.

We present a comprehensive study of short channel effects in organic field-effect transistors by measuring the electrical characteristics of devices with fixed channel width and varying channel length. Our studies are conducted on a hole transport organic semiconductor, E,E-2,5-bis-{4′-bis-(4″-methoxy-phenyl)amino-styryl}-3,4-ethylenedioxy-thiophene, that is spin-coated from solution to form bottom contact organic field-effect transistors. Drain–source currents from transistors with a channel length of 50 μm show excellent agreement with the square law equations derived for crystalline Si MOSFETs in both the linear and saturation regimes. As the channel length is incrementally reduced to 1 μm, device characteristics such as saturation regime channel conductance, sub-threshold current and threshold voltage, behave in a manner similar to Si MOSFETs of decreasing channel length. Results of these studies indicate the presence of non-destructive current punch-through and in addition, behavior similar to channel-length modulation and threshold-voltage roll-off, neither of which have previously been reported in OFETs.

Significant progress has been made in the area of p-type organic field effect transistors while progress in developing n-type materials and devices has been comparatively lacking, a limiting factor in the pursuit to develop complementary organic electronic circuits. Given the need for n-type organic semiconductors we have carried out studies using two different fullerene molecules, C60 and C70. Here, we report mobilities for C60 ranging from 0.02 cm2/V s up to 0.65 cm2/V s (depending on channel length), and mobilities from 0.003 cm2/V s up to 0.066 cm2/V s for C70. All devices were fabricated with organic films deposited under high vacuum but tested at ambient pressures under nitrogen.

We report on self-forming electrode modification by mixing 2,3,4,5,6-pentafluorothiophenol (PFBT) directly into the solution of the organic semiconductor prior to film formation on top of existing metal electrodes. During the formation of the semiconductor layer from the mixed solution, PFBT chemisorbs on the underlying source/drain electrodes and modifies their electronic properties. The modification of evaporated silver, gold, or printed silver electrodes with PFBT is analyzed by X-ray photoelectron spectroscopy. The use of this self-forming electrode modification is applied to solution-processed p-channel top-gate 6,13-bis(triisopropylsilylethynyl)pentacene/poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] organic field-effect transistors (OFETs) that comprise bare silver or gold source/drain electrodes. The proposed new method simplifies device fabrication while yielding OFETs with a performance level that is comparable to that of reference devices in which the metal electrodes are modified with PFBT prior to the fabrication of the semiconductor layer.

We report on reversible changes of the work function (WF) values of indium-tin-oxide (ITO) under prolonged ultraviolet (UV) and air exposure. The WF of ITO is reduced from 4.7 eV to 4.2 eV by photon absorption in ITO under UV illumination or an air mass 1.5 solar simulator (100 mW cm−2). Air or oxygen exposure is found to increase the WF of ITO (UV-exposed) to a value of 4.6 eV. These changes of ITO's WF lead to reversible variations of the performance of organic photovoltaic devices where ITO acts primarily as the electron collecting or hole collecting electrode. These variations can be reflected in the disappearance (or appearance) of an S-shaped kink in the J–V characteristics upon continuous UV or solar simulator illumination (or air exposure). This reversible phenomenon is ascribed to the adsorption and desorption of oxygen on the surface and grain boundaries of ITO. The use of surface modifiers to either decrease or increase the WF of ITO in organic photovoltaic devices with inverted and conventional geometries is also shown to be an effective route to stabilize the device performance under UV illumination.

We review potential applications of third-harmonic generation (THG) in polymer composites to implement optical image processing applications at the eye-safe and technologically relevant telecommunication bands. We discuss two examples, time-gated imaging through scattering media, and image recognition using Fourier-based techniques, where THG in a polymer composite offers significant advantages over typical holographic media, in that it produces signals that are non-degenerate in optical frequency and space, and allows the development of applications that are compatible with low-cost Si-based electronic components.

Six N,N′,5,11-tetrasubstituted coronene-2,3,8,9-tetracarboxydiimides have been synthesised incorporating 3,4,5-tri(n-dodecyloxy)phenyl or 2-(n-decyl)-n-tetradecyl groups in various positions. Differential scanning calorimetry, polarised optical microscopy, and X-ray diffraction indicate that all form columnar discotic mesophases from around room temperature to around 200 °C. Charge-carrier mobility values, which energetic considerations suggest are electron mobility values, have been determined in non-aligned samples cooled from the isotropic melt using the space-charge-limited current technique. The highest mobility, 6.7 cm2V−1 s−1, was found in N,N′-bis(n-2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecylfluorooctyl)-5,11-bis(3-[{3,4,5-tri(n-dodecyloxy)phenyl}carbonyloxy]-n-propyl)coronene-2,3,8,9-tetracarboxydiimide, which X-ray diffraction suggests is the most highly ordered of the materials examined.

The charge-carrier mobilities for three Ni bis(dithiolene) complexes have been determined using the steady-state space-charge limited current technique. A high mobility of 2.8 cm2 V–1 s–1 was observed for one compound, which exhibits a π-stacked columnar structure, in an annealed unsymmetrical melt-processed device. Energy-level considerations and field-effect transistor measurements suggest that this value represents an electron mobility. However, saturation mobilities measured for this compound in spin-coated field-effect transistors were found to be over two orders of magnitude lower than the space-charge limited current values. X-Ray diffraction shows a difference in morphology between thick melt-processed and thin spin-coated films and, therefore, a significant change in intermolecular packing between the device types may explain the discrepancy in mobilities obtained using the two techniques.

We report on the properties of inverted polymer solar cells using an ultrathin Al2O3 buffer layer on indium tin oxide (ITO). The ultrathin Al2O3 layer, deposited by the atomic layer deposition method, was found to reduce the work function of ITO and turns ITO into an electron-collecting electrode. The current density–voltage characteristics of unexposed devices showed an s-shape kink. The kink was eliminated upon exposure to ultraviolet (UV) illumination. Inverted solar cells based on P3HT:PC60BM yielded a fill factor of 0.64 and a power conversion efficiency of about 2.8% estimated for 100 mW cm−2 simulated AM 1.5 illumination.

We investigate the effects of surface modification of indium tin oxide (ITO) on the performance of organic multilayer molecular photovoltaic devices based on pentacene/C60 bi-layer heterojunctions. Values of the open-circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (η) are found invariant of the work function and surface hydrophobicity of ITO. Insensitivity of these parameters to variations of work function in the range of 4.50 to 5.40 eV achieved through the use of surface modifiers are correlated with an invariance of the barrier height (∼0.6 eV) due to Fermi level pinning at the ITO/pentacene interface. Energy barrier heights are extracted independently from the analysis of the electrical characteristics of single-layer diodes based on modified ITO and pentacene using an equivalent circuit model.

A series of highly soluble donor–acceptor (D–A) copolymers containing N-(3,4,5-tri-n-decyloxyphenyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) or N-(2-decyltetradecyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP′) as donor and three different acceptors, 4,7-dithien-2-yl-[2,1,3]-benzothiadiazole, 4,9-dithien-2-yl-6,7-di-n-hexyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 4,8-dithien-2-yl-2λ4δ2-benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole (BThX, X = BTD, TQHx2, BBT, respectively) were synthesized by Stille coupling polymerizations. The optical and electrochemical properties of these copolymers were investigated, along with their use in field-effect transistors and photovoltaic devices. The band gaps (eV) estimated from UV-vis-NIR spectra and electrochemical measurements of the copolymers varied from ca. 1.5–0.5 eV, and were consistent with quantum-chemical estimates extrapolated using density functional theory. Oxidative and reductive spectroelectrochemistry of the copolymers indicated they can be both p-doped and n-doped, and three to four differently colored redox states of the polymers can be accessed through electrochemical oxidation or reduction. The DTP-BThBTD and DTP-BThTQHx2 copolymers exhibited average field-effect hole mobilities of 1.2 × 10−4 and 2.2 × 10−3 cm2/(Vs), respectively. DTP-BThBBT exhibited ambipolar field-effect characteristics and showed hole and electron mobilities of 1.2 × 10−3 and 5.8 × 10−4 cm2/(Vs), respectively. Bulk heterojunction photovoltaic devices made from blends of the copolymers with 3′-phenyl-3′H-cyclopropa[1,9](C60-Ih)[5,6]fullerene-3′-butanoic acid methyl ester (PCBM) (1:3 weight ratio) exhibited average power conversion efficiencies as high as 1.3% under simulated irradiance of 75 mW/cm2.

We report on a systematic study of solvent and polymer matrix effects on the phase segregation behavior of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) blends incorporated into two different amorphous polymer matrices, poly (α-methyl styrene) and poly (triarylamine), and using two solvents, chlorobenzene and tetralin. Optical microscopy, X-ray diffraction analyses, and optical absorption measurements are used to evaluate the film morphology, crystallinity, and optical density, respectively. These analyses are correlated with the extent of vertical segregation of TIPS-pentacene, as observed for the blended films by depth-profile XPS analyses. The microstructure and vertical phase segregation of TIPS-pentacene in blend films are found to be strongly influenced by the choice of solvent. Tetralin, a solvent with a high boiling temperature, was found to be more desirable for achieving distinct phase segregation/crystallization of TIPS-pentacene in blend films and best performance in OFETs with a dual-gate geometry. The electrical properties of top and bottom channels were consistent with the morphological characterization and OFETs processed from tetralin showed higher mobility values than those from chlorobenzene. Further modification of the annealing conditions in the TIPS-pentacene/PTAA/tetralin ternary system led to top-gate OFETs with mobility values up to 2.82 cm2/Vs.

We report on semitransparent air-processed all-plastic solar cells, fabricated from vacuum-free processes, comprising two polymer electrodes, a polymeric work-function modification layer and a polymer:fullerene photoactive layer. The active layer and the top PEDOT:PSS electrode were prepared by sequential film-transfer lamination on polyethylenimine-modified PEDOT:PSS bottom electrodes. The transferring of films offers ease of layer patterning and the misalignment of defects in the different layers resulting from the additive film transfer lamination process yields high shunt resistance values of 108 ohm cm2. Consequently, all-plastic solar cells fabricated with this process exhibit very low reverse bias dark current and can operate in the photovoltaic quadrant with light irradiance varying over five orders of magnitude. The analysis of the values of the open-circuit voltage as a function of light irradiance over that wide dynamic range points toward an ideality factor of n = 1.82 and a reverse saturation current density of 6.2 × 10−11 A cm−2 for solar cells with an active layer comprised of a blend of poly(3-hexylthiophene) and an indene fullerene bis-adduct.