•An ammonia-modified PEDOT:PSS HTLs in inverted PSCs was proposed and demonstrated.•The ion-exchange reaction between PSS-H and CH3NH3I was inhibited by simply doping PEDOT:PSS solution with ammonia.•The enhancement of Voc and PCE for the PSCs using the ammonia-doped PEDOT:PSS HTL was observed.Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) is one of the most widely used hole transport layers (HTL) in inverted perovskite solar cells (PSCs) due to its simple solution-processed ability, high transparency, and conductivity. However, PEDOT:PSS-based devices suffer a lower open-circuit voltage (Voc) than devices with the conventional structure. To address this issue, we fabricated ammonia-modified PEDOT:PSS films by simply doping PEDOT:PSS solution with different ratio of ammonia. The acidity of PEDOT:PSS can be neutralized by the doped ammonia, which inhibits the ion-exchange reaction between PSS-H and CH3NH3I, thus retarding the reduction of the work function for PEDOT:PSS to some extent. As a result, a superior power conversion efficiency (PCE) of 15.5% was obtained for the device based on the ammonia-doped PEDOT:PSS HTL than that of the pristine PEDOT:PSS-based device. We ascribe the PCE enhancement to the increased Voc and fill factor (FF), which is attributed not only to the better energy-level alignment between the ammonia-modified PEDOT:PSS film and perovskite layer but also to the increased grain size and crystallinity of perovskite film.Download high-res image (175KB)Download full-size image

•TiO2/SnOxCly double layer was firstly employed as the electron transport layer (ETL) for planar perovskite solar cells.•TiO2/SnOxCly based devices exhibit reduced hysteresis and remarkable improvement in device efficiency.•TiO2/SnOxCly ETL could enhance electron extraction and reduce surface trap-state.Recently, perovskite solar cells have attracted tremendous research interest due to their amazing light to electric power conversion efficiency (PCE). However, most high performance devices usually use mesoporous TiO2 as the electron transport layer (ETL), which increases cost for practical application. Here, TiO2/SnOxCly double layer was employed as the ETL for planar perovskite solar cells. Compared with bare TiO2, perovskite solar cell based on TiO2/SnOxCly shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO2/SnOxCly which could enhance electron extraction and reduce surface trap-state.TiO2/SnOxCly double layer was employed as the electron transport layer for planar perovskite solar cell. Compared with bare TiO2, perovskite solar cell based on TiO2/SnOxCly shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO2/SnOxCly which could enhance electron extraction and reduce surface trap-state.Download high-res image (253KB)Download full-size image

•New emission color tuning technique of perovskite CH3NH3PbBr3−xClx via annealing was found.•Decreasing annealing temperature of perovskite CH3NH3PbBr3−xClx results in blue shift of PL spectra.•Decomposition of CH3NH3Cl during annealing is the main cause of band narrower under high annealing temperature.A fundamental step to design perovskite light emitting device (PeLED) is to properly control its emission color of lead halide perovskite layer. In this paper, we find the color of perovskite layer can be tunable with the annealing temperature. By decreasing the annealing temperature, a blue shift of emission peak for perovskite CH3NH3PbBr3−xClx layer can be observed. Possible reasons for such phenomena were also investigated. We excluded the affinity difference of CH3NH3Cl and CH3NH3Br to get into perovskite. By synthesizing perovskite powder using precursors heated under vacuum or ambient condition, emission peak can also be tunable, suggesting decomposition of chloride may make contribution to the color tuning.

•Polarizing PSCs are fabricated by liquid crystalline self-organization technique.•PEDOT:PSS alignment layer induces upper PBTTT molecules to orient uniaxially.•The dichroic ratio of oriented PBTTT film is ca. 6.35 at absorption peak.•Polarizing PSCs have more competitive PCE compare to isotropic PSCs.•Parallel excitation produces longer exciton lifetime in uniaxial aggregation.We manufactured polarizing polymer solar cells (PSCs) utilizing a liquid crystalline polymer (i.e., poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT)) as an electron donor material and a material that selectively absorbs polarized light. The oriented PBTTT films prepared using a self-organization process exhibited a high dichroic ratio of ca. 6.35 at the absorption peak. The polarizing PSCs based on oriented PBTTT–PC71BM photoactive layers exhibit an anisotropic photovoltaic effect under polarized illumination along the two orthogonal axes. The polarizing PSCs have a larger power conversion efficiency under parallel-polarized illumination than that of isotropic PV devices under unpolarized illumination. Based on picosecond fluorescent spectra, the parallel excitation produces a slower ground state recovery and a longer exciton lifetime than perpendicular excitation for PBTTT molecules in a uniaxially oriented arrangement.

•A new fullerene derivative PCBAb is used as the acceptor in polymer solar cells.•The electron mobility of PCBAb responds notably to UV and VIS light.•The devices are switched between “active” and “sleep” by UV and VIS treatments.•The PCEs of “active” and “sleep” devices are 2.0% and 0.4% respectively.[6,6]-Phenyl-C61-butyric acid-4′-hydroxyl-azobenzene ester (PCBAb) was synthesized and used as the acceptor in the fabrication of reversible UV–VIS response bi-state polymer solar cells (PSCs) based on the photoinduced cis–trans isomerization of PCBAb. The device can be switched between “active” and “sleep” by the irradiation of UV and visible light, respectively. The active device has a PCE of 2.0%. With UV irradiation, the device goes to “sleep” with a lowered PCE (0.4%), and simultaneously decreased Jsc, Voc and FF, while after visible light treatment, the device is made “active” again. The mechanism of the bi-state process involves the different electron mobilities of the isomers.

Recently, highly efficient solar cells based on organic–inorganic perovskites have been intensively reported for developing fabricating methods and device structures. Additional power conversion efficiency should be gained without increasing the thickness and the complexity of the devices to accord with practical applications. In this paper, a rough interface between perovskite and HTM was fabricated in perovskite solar cells to enhance the light scattering effect and improve the charge transport. The parameters related to the morphology have been systematically investigated by sequential deposition. Simultaneous enhancements of short-circuit current and power conversion efficiency were observed in both CH3NH3PbI3 and CH3NH3PbI3−xClx devices containing the rough interface, with power conversion efficiencies of 10.2% and 10.8%, respectively. Our finding provides an efficient and universal way to control the morphology and further optimize perovskite solar cells for devices by sequential deposition with various structures.

A stable self nano-aggregated bathocuproine film was fabricated and introduced atop of a conventional organic light emitting diode for enhancing top emission. It leads to a 2.7–2.1-fold enhancement on top emission at applied voltage from 4 to 9 V which is much larger than the 1.5–1.3-fold enhancement for a device overlaid with an amorphous bathocuproine film. The more effective outcoupling of this method probably arises from surface plasmon modes being scattered by only the nanostructured surface, and thus without phase cancellation, at the bathocuproine/air boundary. Moreover, this method nearly preserves the original electroluminescent spectra and has no damage on electrical properties.

Since 1987, the possibility of realizing a new generation display based on organic light-emitting diodes (OLEDs) has inspired much interest in both academic and industrial groups. This review elucidates recent process in materials for OLEDs, approaches to improve electroluminescent properties of devices, and recent works based on conjugated materials in our laboratory.

A novel red–orange emitting material with a branched molecular structure, 2,4,6-tris[2-(N-ethyl-3-carbazole)carboxethenyl]-1,3,5-s-triazine (TC3), has been synthesized and characterized using UV–visible, photoluminescence (PL) and electroluminescence (EL) spectroscopy. White EL devices were fabricated using TC3 as a red–orange emitter and 8-hydroxyquinolinolato lithium (Liq) as a blue–green emitter. N,N-bis(3-methylphenyl)-N,N-diphenylbenzidine (TPD) as the adjustor for charge carrier mobility was introduced between the two emitting layers to improve the stability of the white emission color on bias voltage. The EL devices of ITO/poly(N-vinylcarbazole) (PVK):TC3 (56 nm)/TPD (5 nm)/Liq (30 nm)/Mg:Ag exhibited good quality white emission. The Commission Internationale De L’Eclairage chromaticity coordinates are (0.34, 0.39) and are stable on the bias voltage.

The single layer and multilayer undoped light-emitting devices were fabricated using a new soluble phenothiazine-based derivative, poly(3,7-N-octyl phenothiozinyl terephthalylidene) (POPTP). Through the optimization of device structures, the multilayer device has a maximum luminance of 1203 cd/m2 at the bias voltage of 9.3 V, using 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as a hole-blocking layer and tris-(8-hydroxyquinoline)aluminium (Alq3) as a electron-injection/transporting layer. The Commision International de L’Eclairage (CIE) coordinates stabilized at (x, y) = (0.46, 0.53) at various bias voltages. Additionally, the dominant wavelength (λD) of around 575 nm and the color purity of approximately 100% indicated a pure yellow emission property. Therefore, POPTP is a stable candidate material with a pure yellow emission for the undoped organic light-emitting diodes (OLEDs).

We proposed a white light-emitting diode based on a dendritic polyfluorene derivative poly((9,9-dibutyl-2,7-diiodo-9H-fluorene)trisphenylamine) (PDFA) as blue-green emitter and doped it with a fluorescent dye 4-dicyanomethylene-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM) as red emitter. White light was achieved by the incoherent superposition of blue-green emission produced from PDFA and red emission from DCM. The Commission Internationale d’Énclairage chromaticity coordinates of the devices varied from (0.19, 0.22) to (0.39, 0.55) with the increase of DCM concentration (from 0 to 0.2 wt.%).

A novel green emitting material of 2,4,6-Tristriphenylamine-1,3,5-s-triazine (TT3) was synthesized and the organic light-emitting diodes of indium tin oxide (ITO)/TT3/ biphasic calcium phosphate (BCP)/Mg:Ag based on TT3 as the hole transporting and emitting layer were fabricated. The electroluminescent properties were studied. The devices gave pure and bright green light emission peaked at 513 nm and the full width at half maximum of the emission was narrowed by 13.2% compared with the typical green EL device of ITO/TPD:PVK/tris(8-hydroxyquinolinato)aluminium/Mg:Ag, and the brightness was higher than that of the typical device at the same voltage.

Polymer double-layer light-emitting diodes were fabricated with inorganic/organic hybrid composite as hole transporting layer. Two conjugated polymers, poly(9,9-dibutyl)fluorene (PDF) and a dendritic polyfluorene derivative, poly((9,9-dibutyl-2,7-diiodo-9H-fluorene)trisphenylamine) (PDFA) were introduced as light-emitting layer. The former organic double-layer devices showed luminance as high as 833 lm/m2, and the power efficiency reached 0.065 lm/W. The latter showed maximum luminance of 1100 lm/m2 and the quantum efficiency reached 0.104 lm/W. The values were higher than those single-layer devices without inorganic/organic hybrid hole transporting layer (HHTL). The improvement in the electroluminescent properties of these devices was attributed to that the introduction of HHTL enhanced hole injection and balanced the combination of hole and electron injected from anode (ITO) and cathode (Mg:Ag).