Recent advances in the interfacial modification of inverted-type polymer solar cells (PSCs) have resulted from controlling the surface energy of the cathode-modified layer (TiO2 or ZnO) to enhance the short-circuit current (Jsc) or optimizing the contact morphology of the cathode (indium tin oxide or fluorine-doped tin oxide) and active layer to increase the fill factor. Herein, we report that the performance enhancement of PSCs is achieved by incorporating a donor macromolecule copper phthalocyanine (CuPc) as an anode modification layer. Using the approach based on orienting the microstructure evolution, uniformly dispersed island-shaped CuPc spot accumulations are built on the top of PTB7:PC71BM blend film, leading to an efficient spectral absorption and photogenerated exciton splitting. The best power conversion efficiency of PSCs is increased up to 9.726%. In addition to the enhanced light absorption, the tailored anode energy level alignment and optimized boundary morphology by incorporating the CuPc interlayer boost charge extraction efficiency and suppress the interfacial molecular recombination. These results demonstrate that surface morphology induction through molecular deposition is an effective method to improve the performance of PSCs, which reveals the potential implications of the interlayer between the organic active layer and the electrode buffer layer.Keywords: charge extraction; light absorption; morphology induction; orienting microstructure evolution; power conversion efficiency;

A smart interface modification strategy was employed to simultaneously improve short-circuit current density (Jsc) and open-circuit voltage (Voc) by incorporating a poly[(9,9-bis(3′-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene] (PFN) interlayer between a TiO2 film and an active layer, arising from the fact that PFN effectively eliminated the interface barrier between TiO2 and the fullerene acceptor. The work function (WF) of TiO2 was apparently reduced, which facilitated effective electron transfer from the active layer to the TiO2 electron transport layer (ETL) and suppressed charge carrier recombination between contact interfaces. Electron injection devices with and without a PFN interlayer were fabricated to prove the eliminated electron barrier, meanwhile photoluminescence (PL) and time-resolved transient photoluminescence (TRTPL) were measured to probe much easier electron transfer from [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) acceptor to TiO2 ETL, contributing to enhanced Jsc. The shift in vacuum level altered the WF of PC71BM, which enlarged the internal electrical field at the donor/acceptor interface and built-in potential (Vbi) across the device. Dark current characteristics and Mott–Schottky measurements indicated the enhancement of Vbi, benefiting to increased Voc. Consequently, the champion power conversion efficiency for a device with a PFN interlayer of 0.50 mg/mL reached to 7.14%, which is much higher than the PCE of 5.76% for the control device.Keywords: built-in potential; electron transport; interface barrier; interface modification; work function;

To overcome drawbacks of the electron transport layer, such as complex surface defects and unmatched energy levels, we successfully employed a smart semiconductor–metal interfacial nanojunciton in organic solar cells by evaporating an ultrathin Al interlayer onto annealing-free ZnO electron transport layer, resulting in a high fill factor of 73.68% and power conversion efficiency of 9.81%. The construction of ZnO-Al nanojunction could effectively fill the surface defects of ZnO and reduce its work function because of the electron transfer from Al to ZnO by Fermi level equilibrium. The filling of surface defects decreased the interfacial carrier recombination in midgap trap states. The reduced surface work function of ZnO-Al remodulated the interfacial characteristics between ZnO and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM), decreasing or even eliminating the interfacial barrier against the electron transport, which is beneficial to improve the electron extraction capacity. The filled surface defects and reduced interfacial barrier were realistically observed by photoluminescence measurements of ZnO film and the performance of electron injection devices, respectively. This work provides a simple and effective method to simultaneously solve the problems of surface defects and unmatched energy level for the annealing-free ZnO or other metal oxide semiconductors, paving a way for the future popularization in photovoltaic devices.Keywords: carrier recombination; filled surface defects; interface barrier; reduced work function; ZnO-Al nanojunction;

There are two critical strategies to achieve the high photoelectric conversion efficiency of polymer photovoltaic cells: broadening the light absorption spectra of the active layer and efficiently splitting photogenerated excitons with a low probability of recombination. Herein, we demonstrate the improved light trapping and reduced photogenerated exciton recombination probability of the inverted heterojunction solar cells by incorporating C60 fullerene modification. This approach ameliorates traditional multiblend/layer systems, and allows multiple acceptor materials to synergistically work. After the fullerene modification layer was incorporated, the optimal device presents a 25.5% improvement of power conversion efficiency (PCE) up to 9.458% with an open circuit voltage (Voc) of 0.8 V, a short-circuit current (Jsc) of 18.575 mA/cm2, and a fill factor (FF) of 63.4%. This study provides a novel inspiration for the structure development of high-efficiency photovoltaic devices.

Nanostructured carbon is a low-cost, economic, and elementally abundant candidate for manufacturing high-conductivity counter electrodes of organic photoelectric devices. Herein, we prepare onion-like carbon nanosphere:silver (OLCNS:Ag) composite electrodes for efficient, inverted-architecture polymer solar cells (PSCs) via a simple, solution-processed approach. The optical electric field distribution from the OLCNS:Ag nanocomposite layer opens up the possibility of additional light harvesting of the entire visible spectrum resulting from synergies between both components. The large effective specific surface area and high conductivity of OLCNS allow significant charge transfer and collection, resulting in a remarkably enhanced power conversion efficiency (PCE) of 9.81% in PTB7:PC71BM PSCs and 6.95% in PCDTBT:PC71BM PSCs, compared with control devices with PCEs of 7.76 and 5.31%, respectively. These consequences indicate that OLCNS:Ag composite electrodes constitute a valid and versatile method for realizing high-performance organic photovoltaic devices.

•MIL-101(Cr) nanoparticles were HF- free synthesized via hydrothermal method.•A resistive humidity sensor was successfully fabricated.•The humidity sensor shows high sensitivity and rapid response-recovery time.•Humidity sensing mechanism was discussed through complex impedance analysis.Metal organic framework MIL-101(Cr) nanoparticles were successfully HF- free synthesized via hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Nitrogen adsorption-desorption technology. Then resistive humidity sensor was fabricated to investigate humidity sensing properties. The results indicate that the sensor shows high sensitivity and rapid response-recovery time. The impedance changes more than three orders of magnitude in the range of 33–95% RH at 100 Hz. The response time and recovery time are 17 s and 90 s respectively. Finally, the humidity sensing mechanism was discussed through complex impedance analysis. The results illustrate that porous MIL-101(Cr) nanoparticles have great potential to be used as humidity sensing materials.

In this contribution, a series of conducting polyfluorenes (PF) are introduced to improve interface adhesion and boost charge extraction of the TiO2 electron transport layer of inverted polymer solar cells (PSCs). After employing poly (9,9-dihexylfluorenyl-2,7-diyl) (PDF), poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1′,3}-thiadiazole)] (PDFBT), and poly[(4-(5-(7-methyl-9,9-dioctyl-9H-fluoren-2-yl) thiophen-2-yl)-7-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PFTBT) as capping layers, interfacial coherence improvement and energy loss decrease are both achieved, facilitating charge transfer from the active layer to the TiO2 layer. The optimized contact, enhanced electrical conductivity, and reduced internal resistance contribute to increased short-circuit current density and fill factor, leading to an enhanced power conversion efficiency (PCE) from 5.72% up to 7.97%. The employment of the PF capping TiO2 buffer layer provides a promising approach to develop high efficiency PSCs.

•Dual electron transporting layer is used in organic solar cells.•The energy barrier for electron transport is decreased.•The balanced charge transfer of electron and hole is achieved.•Well contact of active layer and cathode is realized.•Electron extraction improvement by a good energy levels tailorment.In this paper, the performance enhancement of organic solar cells based on PCDTBT:PC71BM and P3HT:PC60BM are demonstrated via employing carbon quantum dots (CQD) to modify the metal oxide electron transport layer. The incorporated CQD with carboxylic acid (–COOH) groups could induce self-assembled monolayer (SAM) with TiO2 buffer layer, which lowered the energy barrier for electron transfer and reduced the inherent incompatibility between the metal oxide and organic active layers. Further investigation shows that SAM of TiO2 with CQD can improve the photo-induced exciton dissociation and charge transfer, leading to a low electron accumulation in charge transport layer and a reduced interface recombination loss.

•Ag8GeS6 nanocrystal was prepared by a simple method.•The light harvesting of active layer was greatly enhanced.•The balanced charge transfer of electron and hole is achieved.•The high exciton generation and dissociation rate is realized.•Electron and hole extractions of electrodes were further improved.Novel Ag8GeS6 nanocrystal materials (AGS NCs) have recently earned affectionate attention due to its bulk band-gap of 1.4 eV, which makes it ideal as a broad-spectrum absorber material for both semiconductor photocatalyst and photovoltaic devices. In this paper, we investigated the role of AGS NCs as molecular dopant on solution-processed polymer solar cells (PSCs). Argyrodite AGS NCs was prepared via a colloidal synthesis process using simple inorganic compounds as precursors. Incorporating AGS NCs into PSCs leads to not only improved light absorption of active layer but also increased phase separation of donor and acceptor. Moreover, the doping effect of AGS NCs was also confirmed by nanoscale morphology and photocurrent generation mechanism analysis, revealing that AGS NCs could serve as both exciton dissociation centers and charge transfer medium. This study shows that employment of AGS NCs is a facile way to improve the electrical and optical properties of organic photovoltaic devices.An easily prepared Ag8GeS6 nanocrystal was employed into polymer solar cells to achieve optical and electric properties enhancement.Download high-res image (296KB)Download full-size image

•An efficient solution-processed nanocrystals interlayer was introduced in PSCs to enhance device efficiency.•The electron extraction of cathode was apparently improved.•The light trapping of optimized devices was increased.•The bimolecular recombination was great suppressed and the electron mobility was enhanced.In this paper, a powerful photoconductive interfacial layer was achieved by employing Cd2SSe/ZnS quantum dots (CSSQDs) to modify the electron-transport layers (ETLs) in polymer solar cells (PSCs). With the optimal concentration of CSSQDs and superior film process condition, the power conversion efficiency (PCE) was increased from 4.12% to 6.49% for P3HT:ICBA based device, leading to a tremendous1.6-fold performance enhancement. Moreover, the interlayer of CSSQDs could effectively improve the light absorption, the electron transport and extraction, as well as the better interfacial contact between the ETLs and active layers, accordingly resulting in a higher short-circuit current density, fill factor, and a lower series resistance, respectively. Hence, the introduction of CSSQDs interfacial layer could obtain a remarkably increased performance for the inverted PSCs.

Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ), a strong molecular acceptor, has been proved to be an excellent candidate to achieve the p-type doping effect. When F4-TCNQ is incorporated into a poly(3-hexylthiophene) (P3HT): indene-C60 bisadduct (ICBA) active layer, superior behavior upon inducing polymer donor excited electron transport is demonstrated due to the addition of a deep-lying lowest unoccupied molecular orbital (LUMO) from F4-TCNQ, leading to the realization of organic solar cells (OSCs) with an improved power conversion efficiency (PCE) of 5.83%, accounting for 29.6% enhancement. In the system of active layer, the low LUMO of F4-TCNQ can easily accept electrons, remarkably reducing electron/hole recombination, which contributes to the enhancement of the photoconductivity and charge carrier mobility, resulting in higher short-circuit current density (Jsc), and achieving a more balanced charge carrier transport, as well as an ideal fill factor (FF).

•Polymer dots were introduced into active layer of polymer solar cells to improve efficiency.•The electrical and optical properties were both enhanced.•The exciton dissociation, charge transport, and charge collection were dramatically increased.In this work, poly(9,9-dioctylfluorene)-co-(4,7-di-2-thienyl-2,1,3-benzothiadiazole) (PF-5DTBT) and copolymer poly(styrene-co-maleic anhydride) (PSMA) dots were prepared as additive for active layer doping to enhance the power conversion efficiency (PCE) of organic solar cells (OSCs), which based on poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) and [6,6]-phenyl C71 butyric acid methyl-ester (PC71BM). A high efficiency of 7.40% was achieved due to increase of short-circuit current (Jsc) and fill factor (FF). The operation mechanism of OSCs doping with polymer dots was investigated, which demonstrated that the efficiency enhancement ascribes to improvement of electrical properties, such as exciton generation, exction dissociation, charge transport, and charge collection.

In this paper, high-performance inverted polymer solar cells (PSCs) with a modified cathode buffer layer, titanium dioxide:polyethylenimine (TiO2:PEI), are demonstrated. The TiO2-O-PEI transport layer was fabricated by electrostatically self-assembled monolayers (ESAM) of PEI molecules. Protonated amine functional groups of PEI can combine protons (H+) hydrolyzing from its aqueous solution. Also, PEI could produce ESAM on the surface of hydroxylated TiO2 because of its cationic characteristics. The incorporation of the TiO2-O-PEI layer enhances the photocurrent and power conversion efficiency (PCE) due to the improved interfacial electron transport and extraction of the TiO2-O-PEI surface and the increased light absorption of the active layer. The enhanced PCE, low-cost materials, and solution process of TiO2-O-PEI buffer layers provide a promising method for highly efficient PSCs.Keywords: electron transport and extraction; electrostatically self-assembled monolayers; PEI; polymer solar cells; power conversion efficiency

In this paper, we demonstrate that the efficiency of P3HT:ICBA blend -based organic solar cells (OSCs) was dramatically enhanced by introducing carbon nanoparticles (CNPs) into the active layer. At the optimal doping concentration, the power conversion efficiency (PCE) of doped devices was increased from 4.12% up to 5.90%, accounting for a 43.20% PCE enhancement. CNPs serve as scattering centers to enlarge the light pathways, resulting in light-harvesting improvements. Meanwhile, the incorporation of CNPs in P3HT:ICBA blend can form a perfect homogeneous interpenetrating network, which is beneficial to improve exciton dissociation, charge transport, charge collection, and the photoconductive property of solar cells. This study establishes an efficient method for fabricating high-performance OSCs based on commercially available donor and acceptor materials.Keywords: Charge collection; Charge transport; Exciton dissociation; Exciton generation; Impedance; Light absorption; Mobility;

Enhanced performance of polymer solar cells (PSCs) based on the blend of poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT):[6,6]-phenyl-C70-butyric acid methyl ester (PC71BM) is demonstrated by titanium dioxide (TiO2) interface modification via CuInS2/ZnS quantum dots (CZdots). Devices with a TiO2/CZdots composite buffer layer exhibit both a high short-circuit current density (Jsc) and fill factor (FF), leading to a power conversion efficiency (PCE) up to 7.01%. The charge transport recombination mechanisms are investigated by an impedance behavior model, which indicates that TiO2 interfacial modification results in not only increasing the electron extraction but also reducing impedance. This study provides an important and beneficial approach to develop high efficiency PSCs.

The reproducible silylation of titanium oxide (TiO2) with small molecular (dichloromethyl) dimethylchlorosilane (DCS) as the cathode buffer layer was developed to improve electron extraction. Through incorporating the DCS capping layer into polymer solar cells (PSCs), the interfacial coherence of devices could be enhanced, leading to a shift in nanocrystallite size and a smaller internal charge transport resistance. Furthermore, a TiO2/DCS combined interfacial layer could serve as both an exciton dissociation center and a charge transfer channel, which results in a reduction in the energy barrier and electron loss, improving hole-blocking and surface-state passivation in the TiO2 interfacial layer. The Kelvin probe measurements demonstrate that the employment of the DCS nanolayer decreases conduction band energy of TiO2via forming a dipole layer at the interface of TiO2 and the DCS nanolayer, which tunes the work-function of the device and ulteriorly enhances charge carrier transfer between the electrode and the active layer. As a result, the photocurrent and the fill factor of the PSCs are both increased, resulting in an increased power conversion efficiency (PCE) of 6.959%.

•Carbon nanodots is incorporated in PEI to improve electron transfer property of polymer solar cell.•Short-circuit current and light harvesting are both improved by introducing carbon nanodots.•The exciton dissociation, charge transfer, and charge collection are greatly enhanced.The performance of polymer solar cells is substantially enhanced by introducing carbon nanodots as additives in polyethylenimine buffer layer. The most pronounced effect is observed in one type of device with the average power conversion efficiencies increased from 5.78% to 7.56% after the addition of carbon nanodots at an optimal concentration in the interfacial layer, which is mainly attributed to the enhanced light trapping and electron transfer in the devices. Besides the light-harvesting and electron transport capacity improvement, the addition of carbon nanodots can also increase exciton generation and dissociation, leading to a high electron mobility. This study demonstrates a facile approach for enhancing the efficiencies of polymer solar cells.Carbon nanodots have been synthesized and incorporated into PEI buffer layer to improve efficiency of polymer bulk heterojunction solar cells. The results show that electron transporting property is apparently enhanced while corresponding open-circuit voltage maintained, leading to an increase of power conversion efficiency.

It has been widely reported that plasmonic effects of metallic nanomaterials can enhance light-harvesting in polymer solar cells (PSCs). However, the improved light trapping degree is closely related to the shape of the nanoparticles (NPs), which inevitably limits the efficiency enhancement for PSCs. In this paper, we demonstrate that the incorporation of Au arrowhead nanorods (AHNRs) into the active layer of inverted PSCs can dramatically lead to a 28.7% efficiency enhancement as compared to preoptimize control PSCs. Both theoretical and experimental results show that the origin of the improved power conversion efficiency (PCE) can be attributed to not only the optical absorption enhancement but also charge transport capacity improvement. The metal tip of AHNRs can lead to a significant enhancement of local field and long-range scattering. In addition, a wide-band absorption improvement is observed, and charge carrier mobilities increase by an order of magnitude. These results offer an effective approach to enhance the efficiency for PSCs.

In this article, we introduce a new method to assist hole extraction by incorporating carbon nanodots (CNDs) interfacial layer between active layer and hole-transporting layer for organic solar cells (OSCs). Under an optimal concentration of CNDs and specific film-forming conditions, a simultaneous enhancement of short-circuit current density (JSC) and fill factor (FF) was achieved, leading to the optimal power conversion efficiency up to 7.22%. Due to the nice conductivity of CNDs, the interlayer effectively bridged the separated islands of active layer to transport free charge carriers toward correct electrodes and reduced charge carrier recombination. The employment of interface modification depicted here can also provide a rough and uniform surface coating on polymer photolayer, leading to improved morphology and closer interface contact, and thus reduce the series resistance and increase FF of OSCs. In addition, the incorporation of CNDs also increased the light-harvesting of active layer. Therefore, the CNDs interfacial layer could play a dual role in the improvement of optical and electrical properties for OSCs.

This Research Article describes a cooperative plasmonic effect on improving the performance of organic solar cells. When Au nanorods(NRs) are incorporated into the active layers, the designed project shows superior enhanced light absorption behavior comparing with control devices, which leads to the realization of organic solar cell with power conversion efficiency of 6.83%, accounting for 18.9% improvement. Further investigations unravel the influence of plasmonic nanostructures on light trapping, exciton generation, dissociation, and charge recombination and transport inside the thin films devices. Moreover, the introduction of high-conductivity Au NRs improves electrical conductivity of the whole device, which contributes to the enhanced fill factor.Keywords: Au nanorods; charge transport; exciton generation; organic solar cells; plasmonic effect; scattering effect;

Cadmium selenide (CdSe) quantum dots (QDs) utilized as additives have been incorporated intopolymer solar cells (PSCs) composed of poly[N-9′′-hepta-decanyl-2,7-carbazolealt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-ben-zothiadiazole)] (PCDTBT) and fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The maximum power conversion efficiency (PCE) of 6.94% has been achieved, corresponding to 33% enhancement compared with the control devices. The introduction of CdSe QDs allows not only the improvement of charge transport properties but also tuning of the energy levels, which leads to a higher short circuit current (Jsc), fill factor (FF), and open-circuit voltage (Voc).

In this study, molecular doping with polymer dots was designed to unravel its effect on the photoconductivity in organic solar cells. The photocurrent in organic solar cells exhibited a considerable increase under optimal doping concentration, leading to an ultimate enhancement of power conversion efficiency from 2.30% to 3.64%. This can be attributed primarily to the improvement of the initial boost in charge carriers due to the background carriers induced by the polymer dots and increased tail absorption by the active layer. Based on single carrier device and impedance measurements, polymer dopant can efficiently decrease charge recombination and improve charge carriers mobilities. The obtained achievements pave an approach of molecular doping in affecting the operation of organic solar cells.

•Phosphor nanoparticles doped in TiO2 film improve polymer solar cell performance.•Short-circuit current and FF improved by phosphor nanoparticles dopant, giving 6.83% efficiency.•Phosphor nanoparticles improve light harvesting and charge transport property.Phosphor materials can be applied to enhance the energy conversion efficiency of a solar cell. Such materials convert low-energy transmitted photons to higher-energy photons that can be absorbed by the cell, substantially decreasing the spectral mismatch between the cell and the solar spectrum. In this paper, the efficiency of organic solar cells (OSCs) was improved by incorporating phosphor nanoparticles as dual functionality into TiO2 cathode buffer layer. The dependence of devices performance on doping concentration of NaYF4:Yb3+,Er3+ nanoparticles was investigated. A high power conversion efficiency of 6.83% was achieved, which mainly attributes to the increase of short-circuit density. The absorption spectrum indicates that light-harvesting of doped films is higher than undoped film, which originates from scattering effect and NIR spectrum sensitization of phosphor nanoparticles. The measurement of electron-only devices shows that electron transport property of doped devices was apparently improved. Impedance spectroscopy reveals that the diffusion coefficient and carrier mobility were greatly enhanced. This study demonstrates that phosphor nanoparticles doping is useful for fabricating high performance OSCs.The light-harvesting and electron carrier transport property are greatly improve by introduction of phosphor nanoparticles.

This article describes a positive effect on improving the performance of organic solar cells (OSCs) by introducing a series of water-soluble polyfluorene (PF) dots. When poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-1-thiadiazole)] (PF1), poly(9,9-dioctylfluorenyl-2,7-diyl) (PF2), and poly(9,9-dioctylfluorene)-co-(4,7-di-2-thienyl -2,1,3-benzothiadiazole) (PF3) dots are mixed into the polyethylenimine (PEI) cathode buffer layer, active layer and PEI films show an enhancement on light absorption in comparison with control film, which leads to the realization of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solar cells with power conversion efficiency (PCE) of 4.33% for PF1 doping, 4.49% for PF2 doping, and 4.72% for PF3 doping, accounting for 23.0%, 27.6%, and 34.1% enhancement, respectively. Simultaneously, doping of PF dots also contributes to the improvement of exciton dissociation, charge transport, and charge collection. PF dots could be used as a dual functional additive to enhance optical and electrical properties for OSCs.

The utilization of inorganic nanocrystals is one of the key strategies to improve the performance of polymer solar cells (PSCs). In this paper, CuInS2/ZnS (CIS-Z) quantum dots (QDs) were employed to improve efficiency of PSCs composed of poly [N-9″-hepta-decanyl-2,7-carbazolealt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-ben-zothiadiazole)](PCDTBT)/fullerene derivative [6,6]-phenyl-C70-butyric acid methyl ester (PC71BM). The maximum power conversion efficiency of 7.19% was achieved, accounting for 21.6% enhancement compared to the control device. The incorporation of CIS-Z QDs allowed not only enhancing exciton generation and dissociation but also improving charge transport property, leading to a higher short-circuit current density and fill factor.

•A broadband absorption of PSC is realized by combining bifunctional NaYF4:Yb3+, Er3+ nanocrystals into the active layer.•For the NaYF4:Yb3+, Er3+ NCs-doped PSCs, enhancement of the Jsc value is approximately 8.68%.•Our studies show that the broadband resonance is achieved by the simultaneous excitation of scattering resonances and UC effect.NaYF4:Yb3+, Er3+ nanocomposites (NCs) are synthesized by a facile solvothermal approach and doped into PCDTBT:PCBM blend as a bifunctional additive to improve peformance of inverted polymer bulk heterojunction (BHJ) solar cells. The dependence of device performance on NaYF4:Yb3+, Er3+ NCs in the blend film is investigated. The results show that the short-circuit current density is apparently enhanced by doping NaYF4:Yb3+, Er3+ NCs into the active layer while maintaining the open-circuit voltage and fill factor, leading to an increase in power conversion efficiency. NaYF4:Yb3+, Er3+ NCs acts two kinds of roles for light absorption enhancement. Up-conversion (UC) emission from Yb3+ sensitized Er3+ dopants in the NaYF4:Yb3+, Er3+ NCs is observed. The photocurrent generated from UC near 980 nm excitation can improve the utilization of solar photons in the near infrared (NIR). The scattering effect of NaYF4 nanoparticles (NPs) enhances the light absorption in visible region. The performance of polymer solar cell doped with NaYF4:Yb3+, Er3+ NCs is compared with that of undoped. The concept of integrating UC and scattering functionality into active layer suggests a promising and practical pathway for improving visible and NIR absorption of polymer solar cells.In this paper, for the first time, a broadband absorption of PSC is realized by combining bifunctional NaYF4:Yb3+, Er3+ nanocrystals exhibiting scattering and UC effect into the active layer. For the NaYF4:Yb3+, Er3+ NCs-doped PSCs, enhancement of the Jsc value for NaYF4:Yb3+, Er3+ NCs is approximately 8.68%, compared to the optimized control PSC. As a result, the mixed NaYF4:Yb3+, Er3+ NCs device shows a high efficiency. For the origin of the enhancement, our theoretical and experimental studies show that the broadband resonance is achieved by the simultaneous excitation of versatile scattering resonances and UC effect.

•Polymer quantum dots are got by a facile approach and doped into active layer as a bifunctional additive.•The short-circuit current and fill factor are both enhanced, leading to an 23.8% increase in power conversion efficiency.•PFDTBT QDs can enhance the utilization of UV light and improve charge carrier transport properties of OSCs.Poly{[2,7-(9-(20-ethylhexyl)-9-hexyl-fluorene])-alt-[5,50-(40,70-di-2-thienyl-20,10,30-benzothid-iazole)]} (PFDTBT) quantum dots (QDs) is synthesized by a facile approach and doped into organic solar cells (OSCs). The dependence of device performance on PFDTBT QDs in the blend film is investigated. The results show that short-circuit current density (Jsc) is apparently enhanced while corresponding open-circuit voltage maintained, leading to an increase in power conversion efficiency (PCE). Maximum PCE of 6.81% is obtained, corresponding to a 23.8% enhancement compared with the undoped device. PFDTBT QDs can act as two kinds of role for improvement of OSCs’ performance: one is improving the utilization ratio of ultraviolet light; the other is effectively improving charge transport property.

•NaYF4 nanoparticles are synthesized by a facile approach and doped into PSCs.•The light absorption is enhanced in visible and IR region.•The short circuit density and power conversion efficiency are both improved.•The performance improvement of PSCs is attributed to the scattering and up-conversion effect.Sodium yttrium fluoride (NaYF4) nanoparticles (NPs) have been used to enhance the performance of optoelectronic devices such as polymer solar cells (PSCs). In this paper, we propose and demonstrate short circuit density (Jsc) enhancement induced by scattering and up-conversion (UC) effect of NPs in PSCs. The NaYF4 NPs were doped in active layer, functioning as highly efficient additive for improving the light harvesting, which leads to significantly increased photocurrent and power conversion efficiency (PCE) of inverted PSCs. The absorption spectrum shows that the doping devices have much stronger absorption, which is in accord with IPCE and transmittance spectrum. The absorption and electric field profile of the devices with or without NaYF4 NPs were performed using finite difference time domain (FDTD) simulation. It is approved that the NaYF4 NPs result in the absorption improvement by scattering and UC effect.

Enhanced performance of polymer solar cells (PSCs) based on the blend of poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT):[6,6]-phenyl-C70-butyric acid methyl ester (PC71BM) is demonstrated by titanium dioxide (TiO2) interface modification via CuInS2/ZnS quantum dots (CZdots). Devices with a TiO2/CZdots composite buffer layer exhibit both a high short-circuit current density (Jsc) and fill factor (FF), leading to a power conversion efficiency (PCE) up to 7.01%. The charge transport recombination mechanisms are investigated by an impedance behavior model, which indicates that TiO2 interfacial modification results in not only increasing the electron extraction but also reducing impedance. This study provides an important and beneficial approach to develop high efficiency PSCs.

In this study, molecular doping with polymer dots was designed to unravel its effect on the photoconductivity in organic solar cells. The photocurrent in organic solar cells exhibited a considerable increase under optimal doping concentration, leading to an ultimate enhancement of power conversion efficiency from 2.30% to 3.64%. This can be attributed primarily to the improvement of the initial boost in charge carriers due to the background carriers induced by the polymer dots and increased tail absorption by the active layer. Based on single carrier device and impedance measurements, polymer dopant can efficiently decrease charge recombination and improve charge carriers mobilities. The obtained achievements pave an approach of molecular doping in affecting the operation of organic solar cells.

The reproducible silylation of titanium oxide (TiO2) with small molecular (dichloromethyl) dimethylchlorosilane (DCS) as the cathode buffer layer was developed to improve electron extraction. Through incorporating the DCS capping layer into polymer solar cells (PSCs), the interfacial coherence of devices could be enhanced, leading to a shift in nanocrystallite size and a smaller internal charge transport resistance. Furthermore, a TiO2/DCS combined interfacial layer could serve as both an exciton dissociation center and a charge transfer channel, which results in a reduction in the energy barrier and electron loss, improving hole-blocking and surface-state passivation in the TiO2 interfacial layer. The Kelvin probe measurements demonstrate that the employment of the DCS nanolayer decreases conduction band energy of TiO2via forming a dipole layer at the interface of TiO2 and the DCS nanolayer, which tunes the work-function of the device and ulteriorly enhances charge carrier transfer between the electrode and the active layer. As a result, the photocurrent and the fill factor of the PSCs are both increased, resulting in an increased power conversion efficiency (PCE) of 6.959%.

Cadmium selenide (CdSe) quantum dots (QDs) utilized as additives have been incorporated intopolymer solar cells (PSCs) composed of poly[N-9′′-hepta-decanyl-2,7-carbazolealt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-ben-zothiadiazole)] (PCDTBT) and fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The maximum power conversion efficiency (PCE) of 6.94% has been achieved, corresponding to 33% enhancement compared with the control devices. The introduction of CdSe QDs allows not only the improvement of charge transport properties but also tuning of the energy levels, which leads to a higher short circuit current (Jsc), fill factor (FF), and open-circuit voltage (Voc).

In this contribution, a series of conducting polyfluorenes (PF) are introduced to improve interface adhesion and boost charge extraction of the TiO2 electron transport layer of inverted polymer solar cells (PSCs). After employing poly (9,9-dihexylfluorenyl-2,7-diyl) (PDF), poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1′,3}-thiadiazole)] (PDFBT), and poly[(4-(5-(7-methyl-9,9-dioctyl-9H-fluoren-2-yl) thiophen-2-yl)-7-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PFTBT) as capping layers, interfacial coherence improvement and energy loss decrease are both achieved, facilitating charge transfer from the active layer to the TiO2 layer. The optimized contact, enhanced electrical conductivity, and reduced internal resistance contribute to increased short-circuit current density and fill factor, leading to an enhanced power conversion efficiency (PCE) from 5.72% up to 7.97%. The employment of the PF capping TiO2 buffer layer provides a promising approach to develop high efficiency PSCs.

Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ), a strong molecular acceptor, has been proved to be an excellent candidate to achieve the p-type doping effect. When F4-TCNQ is incorporated into a poly(3-hexylthiophene) (P3HT): indene-C60 bisadduct (ICBA) active layer, superior behavior upon inducing polymer donor excited electron transport is demonstrated due to the addition of a deep-lying lowest unoccupied molecular orbital (LUMO) from F4-TCNQ, leading to the realization of organic solar cells (OSCs) with an improved power conversion efficiency (PCE) of 5.83%, accounting for 29.6% enhancement. In the system of active layer, the low LUMO of F4-TCNQ can easily accept electrons, remarkably reducing electron/hole recombination, which contributes to the enhancement of the photoconductivity and charge carrier mobility, resulting in higher short-circuit current density (Jsc), and achieving a more balanced charge carrier transport, as well as an ideal fill factor (FF).

The surface plasmon resonance (SPR) effect of metal nanoparticles is widely employed in organic solar cells to enhance device performance. However, the light-harvesting improvement is highly dependent on the shape of the metal nanoparticles. In this study, the significantly enhanced performance upon incorporation of Au nanoarrows in solution-processed organic photovoltaic devices is demonstrated. Incorporating Au nanoarrows into the ZnO cathode buffer layer results in superior broadband optical absorption improvement and a power conversion efficiency of 7.82% is realized with a 27.3% enhancement compared with the control device. The experimental and theoretical results indicate that the introduction of Au nanoarrows not only increases optical trapping by the SPR effect but also facilitates exciton generation, dissociation, and charge transport inside the thin film device.