lizhendong

A new, easy, and efficient approach is reported to enhance the driving force for charge transfer, break tradeoff between open-circuit voltage and short-circuit current, and simultaneously achieve very small energy loss (0.55 eV), very high open-circuit voltage (>1 V), and very high efficiency (>10%) in fullerene-free organic solar cells via an energy driver.

While indirectly patterned organic–inorganic hybrid perovskite nanostructures have been extensively studied for use in perovskite optoelectronic devices, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high-temperature environments. Here, a simple and low-cost approach is proposed to directly pattern perovskite solid-state films into periodic nanostructures. The approach is basically perovskite recrystallization through phase transformation with the presence of a periodic mold on an as-prepared solid-state perovskite film. Interestingly, this study simultaneously achieves not only periodically patterned perovskite nanostructures but also better crystallized perovskites and improved optical properties, as compared to its thin film counterpart. The improved optical properties can be attributed to the light extraction and increased spontaneous emission rate of perovskite gratings. By fabricating light-emitting diodes using the periodic perovskite nanostructure as the emission layers, approximately twofold higher radiance and lower threshold than the reference planar devices are achieved. This work opens up a new and simple way to fabricate highly crystalline and large-area perovskite periodic nanostructures for low-cost production of high-performance optoelectronic devices.

A new and simple direct nanopatterning approach for fabricating highly crystalline and large-area periodic perovskite nanostructures is proposed. This approach is suitable for preparing perovskite nanostructures with different configurations. More importantly, the prepared periodic perovskite nanostructures can be fabricated into different optoelectronic devices, such as solar cells, light-emitting diodes, laser diodes, and photodetectors.

A polydimethylsiloxane cylindrical-hole-template-confined solution-growth method is developed to fabricate densely packed CsPbCl_{3− x} Br _x microdisk laser arrays. Furthermore, a strategy to integrate multicolored microdisk laser (MDL) arrays is demonstrated that simultaneously lase in the deep blue, blue, cyan, and green by means of gas-phase replacement of Cl by Br from initial CsPbCl₃ MDLs in HBr vapor.

Highly efficient organic/inorganic hybrid perovskite light-emitting diodes (PeLEDs) based on graphene anode are developed for the first time. Chemically inert graphene avoids quenching of excitons by diffused metal atom species from indium tin oxide. The flexible PeLEDs with graphene anode on plastic substrate show good bending stability; they provide an alternative and reliable flexible electrode for highly efficient flexible PeLEDs.

A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by room-temperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g⁻¹.

Silicon/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) heterojunction solar cells with 16.2% efficiency and excellent stability are fabricated on pyramid-textured silicon substrates by applying a water-insoluble ester as capping layer. This shows that a conformal coating of PEDOT:PSS on textured silicon can greatly improve the junction quality with the main stability failure routes related to the moisture-induced poly(3,4-ethylenedioxythiophene) aggregations and the tunneling silicon oxide autothickening.

Easily accessible tetra-5-hexylthiophene-, tetra-5-hexyl-2,2′-bisthiophene-substituted zinc phthalocyanines (ZnPcs) and tetra-tert-butyl ZnPc are employed as hole-transporting materials in mixed-ion perovskite [HC(NH₂)₂]_0.85(CH₃NH₃)_0.15Pb(I_0.85Br_0.15)₃ solar cells, reaching the highest power conversion efficiency (PCE) so far for phthalocyanines. Results confirm that the photovoltaic performance is strongly influenced by both, the individual optoelectronic properties of ZnPcs and the aggregation of these tetrapyrrolic semiconductors in the solid thin film. The optimized devices exhibit PCE of 15.5% when using tetra-5-hexyl-2,2′-bisthiophene substituted ZnPcs, 13.3% for tetra-tert-butyl ZnPc, and a record 17.5% for tetra-5-hexylthiophene-based analogue under standard global 100 mW cm⁻² AM 1.5G illumination. These results boost up the potential of solution-processed ZnPc derivatives as stable and economic hole-transport materials for large-scale applications, opening new frontiers toward a realistic, efficient, and inexpensive energy production.

Easily accessible tetra-5-hexylthiophene-, tetra-5-hexyl-2,2′-bisthiophene-, and tetra-tert-butyl-substituted zinc phthalocyanines (ZnPcs) are employed as hole-transporting materials in mixed-ion perovskite [HC(NH₂)₂]_0.85(CH₃NH₃)_0.15Pb(I_0.85Br_0.15)₃ solar cells, reaching record power conversion efficiency of 17.5% under standard global AM 1.5G irradiation. The data highlight the potential large-scale applications of solution-processed ZnPc derivatives as stable and economic hole-transport materials for perovskite solar cells.

In article 1604044, T. Wang and co-workers report compositional and surface modifications to low-temperature-processed TiO₂ films as electron transport layers in inverted polymer solar cells. This approach not only increases the power conversion efficiency of photovoltaic devices to 10.5%, but more importantly, eliminates the light-soaking problem that is commonly observed in polymer solar cells employing metal oxides as the charge-transport layers.

A novel wide-gap conjugated polymer PhF2,5 (E_g = 1.9 eV) is designed to contain alternating cyclopentadithiophene and difluorophenylene unit with the goal of favoring unipolar organic field effect transistor characteristics. The higher lowest unoccupied molecular orbital energy of PhF2,5 increases the barrier to electron injection, leading to unipolar transport and higher on/off ratios, without sacrificing desirable high hole mobilities.

Organic–inorganic perovskite photovoltaics are an emerging solar technology. Developing materials and processing techniques that can be implemented in large-scale manufacturing is extremely important for realizing the potential of commercialization. Here we report a hot-casting process with controlled Cl⁻ incorporation which enables high stability and high power-conversion-efficiencies (PCEs) of 18.2% for small area (0.09 cm²) and 15.4% for large-area (≈1 cm²) single solar cells. The enhanced performance versus tri-iodide perovskites can be ascribed to longer carrier diffusion lengths, improved uniformity of the perovskite film morphology, favorable perovskite crystallite orientation, a halide concentration gradient in the perovskite film, and reduced recombination by introducing Cl⁻. Additionally, Cl⁻ improves the device stability by passivating the reaction between I⁻ and the silver electrode. High-quality thin films deployed over a large-area 5 cm × 5 cm eight-cell module have been fabricated and exhibit an active-area PCE of 12.0%. The feasibility of material and processing strategies in industrial large-scale coating techniques is then shown by demonstrating a “dip-coating” process which shows promise for large throughput production of perovskite solar modules.

A hot-casting perovskite processing technique with controlled Cl⁻ incorporation affords a high power conversion efficiency of 18.2% for small-area (0.09 cm²), 15.4% for large-area (≈1 cm²) single solar cells, and 12.0% for large-area 5 cm × 5 cm eight-cell modules and compatibility with large throughput production techniques.

Efficient ternary polymer solar cells are constructed by incorporating an electron-deficient chromophore (5Z,5′Z)-5,5′-((7,7′-(4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(6-fluorobenzo[c][1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) (IFBR) as an additional component into the bulk-heterojunction film that consists of a wide-bandgap conjugated benzodithiophene-alt-difluorobenzo[1,2,3]triazole based copolymer and a fullerene acceptor. With respect to the binary blend films, the incorporation of a certain amount of IFBR leads to simultaneously enhanced absorption coefficient, obviously extended absorption band, and improved open-circuit voltage. Of particular interest is that devices based on ternary blend film exhibit much higher short-circuit current densities than the binary counterparts, which can be attributed to the extended absorption profiles, enhanced absorption coefficient, favorable film morphology, as well as formation of cascade energy level alignment that is favorable for charge transfer. Further investigation indicates that the ternary blend device exhibits much shorter charge carrier extraction time, obviously reduced trap density and suppressed trap-assisted recombination, which is favorable for achieving high short-circuit current. The combination of these beneficial aspects leads to a significantly improved power conversion efficiency of 8.11% for the ternary device, which is much higher than those obtained from the binary counterparts. These findings demonstrate that IFBR can be a promising electron-accepting material for the construction of ternary blend films toward high-performance polymer solar cells.

A nonfullerene acceptor (5Z,5′Z)-5,5′-((7,7′-(4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(6-fluorobenzo[c]-[1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) is introduced as an electron-cascade acceptor material in blends of a wide-bandgap donor poly(benzodithiophene-alt-difluorobenzo[1,2,3]triazole) and a fullerene acceptor [6,6]-phenyl-C₆₁-butyric acid methyl ester to fabricate ternary blend polymer solar cells (PSCs). The ternary device exhibits a power conversion efficiency of 8.11%, which is much higher than those obtained from the binary PSCs.

The generation efficiency of long-lived photoinduced charges in polymer:fullerene bulk heterojunctions increases dramatically as the strength of intermolecular electronic coupling in the fullerene phase improves. Ultrafast geminate recombination is suppressed when electron delocalization within fullerene clusters is strong, while the opposite is observed when delocalization within the cluster is poor. In article number 1601427, Garry Rumbles and co-workers show that the molecular design of the fullerene not only determines inter-fullerene electronic coupling, but also influences the decay dynamics of free holes in the donor phase even when the polymer microstructure remains unchanged.

The influence of illumination on the long-term performance of planar structured perovskite solar cells (PSCs) is investigated using fast and spatially resolved luminescence imaging. The authors analyze the effect of illuminated current density–voltage (J–V) and light-soaking measurements on pristine PSCs by providing visual evidence for the spatial inhomogeneous evolution of device performance. Regions that are exposed to light initially produce stronger electroluminescence signals than surrounding unilluminated regions, mainly due to a lower contact resistance and, possibly, higher charge collection efficiency. Over a period of several days, however, these initially illuminated regions appear to degrade more quickly despite the device being stored in a dark, moisture- and oxygen-free environment. Using transmission electron microscopy, this accelerated degradation is attributed to delamination between the perovskite and the titanium dioxide (TiO₂) layer. An ion migration mechanism is proposed for this delamination process, which is in accordance with previous current–voltage hysteresis observations. These results provide evidence for the intrinsic instability of CH₃NH₃PbI₃-based devices under illumination and have major implications for the design of PSCs from the standpoint of long-term performance and stability.

Temporal behavior of a selectively illuminated region in perovskite solar cells is tracked using photoluminescence (PL) and electroluminescence (EL) imaging. Although initially the EL (PL) intensity shows noticeable enhancement (reduction) in the illuminated region, it deteriorates (improves) over time relative to the non-illuminated surroundings. Combined with cross-sectional transmission electron microscopy, bias-induced perovskite/TiO₂ interfacial electrical and/or physical decoupling is demonstrated.

In this work, both anode and cathode interfaces of p-i-n CH₃NH₃PbI₃ perovskite solar cells (PVSCs) are simultaneously modified to achieve large open-circuit voltage (V_oc) and fill factor (FF) for high performance semitransparent PVSCs (ST-PVSCs). At the anode, modified NiO serves as an efficient hole transport layer with appropriate surface property to promote the formation of smooth perovskite film with high coverage. At the cathode, a fullerene bisadduct, C₆₀(CH₂)(Ind), with a shallow lowest unoccupied molecular orbital level, is introduced to replace the commonly used phenyl-C₆₁-butyric acid methyl ester (PCBM) as an alternative electron transport layer in PVSCs for better energy level matching with the conduction band of the perovskite layer. Therefore, the V_oc, FF and power conversion efficiency (PCE) of the PVSCs increase from 1.05 V, 0.74 and 16.2% to 1.13 V, 0.80 and 18.1% when the PCBM is replaced by C₆₀(CH₂)(Ind). With the advantages of high V_oc and FF, ST-PVSCs are also fabricated using an ultrathin transparent Ag as cathode, showing an encouraging PCEs of 12.6% with corresponding average visible transmittance (AVT) over 20%. These are the highest PCEs reported for ST-PVSCs with similar AVTs paving the way for using ST-PVSCs as power generating windows.

The anode and cathode interfaces of CH₃NH₃PbI₃ perovskite solar cells are optimized simultaneously. The shallow lowest unoccupied molecular level of C₆₀(CH₂)(Ind) provides better energy level alignment and surface passivation. High performance opaque cell with a power conversion efficiency (PCE) of 18.1% (V_oc: 1.13 V, FF: 0.8) and semitransparent cell with a PCE of 12.6% (AVT>20%) are achieved.

The synthesis and growth of perovskite films with controlled crystallinity and microstructure for highly efficient and stable solar cells is a critical issue. In this work, thiourea is introduced into the CH₃NH₃PbI₃ precursor with two-step sequential ethyl acetate (EA) interfacial processing. This is shown for the first time to grow compact microsized and monolithically grained perovskite films. X-ray diffraction patterns and infrared spectroscopy are used to prove that thiourea significantly impacts the perovskite crystallinity and morphology by forming the intermediate phase MAI·PbI₂·SC(NH₂)₂. Afterward, the residual thiourea which coursed charge recombination is completely extracted by the sequential EA processing. The product has improved light harvesting, suppressed defect state, and enhanced charge separation and transport. The sequentially EA processed perovskite solar cells offer an impressive 18.46% power conversion efficiency and excellent stability in ambient air. More importantly, the EA postprocessed perovskite solar cells also have excellent voltage response under ultraweak light (0.05% sun) with promising utility in photodetectors and photoelectric sensors.

A new perovskite precursor and a two-step antisolvent processing method are utilized to grow monolithically grained perovskite films. The as-prepared films have achieved enhanced light absorption, suppressed surface defect level, and accelerated charge separation and transport. The power conversion efficiency of the solar cells reaches 18.46% with much optimized stability, repeatability, and voltage responsibility.

Diketopyrrolopyrrole (DPP)-based polymers have been consistently used for the fabrication of solar cell devices and transistors due to the existence of intermolecular short contacts, resulting in high electron and hole mobilities. However, they also often show limited external quantum efficiencies (EQEs). In this contribution, the authors analyze the limitations on EQE by a combined study of exciton dissociation efficiency, charge separation, and recombination kinetics in thin films and solar devices of a DPP-based donor polymer, DPPTT-T (thieno[3,2-b]thiophene-diketopyrrolopyrrole copolymer) blended with varying weight fractions of the fullerene acceptor PC₇₀BM. From the correlations between photoluminescence quenching, transient absorption studies, and EQE measurements, it is concluded that the main limitation of photon-to-charge conversion in DPPTT-T/PC₇₀BM devices is poor exciton dissociation. This exciton quenching limit is related not only to the low affinity/miscibility of the materials, as confirmed by wide angle X-ray diffraction diffraction and transmission electron microscopy data, but also to the relatively short DPPTT-T singlet exciton lifetime, possibly associated with high nonradiative losses. A further strategy to improve EQE in this class of polymers without sacrificing the good extraction properties in optimized blends is therefore to limit those nonradiative decay processes.

Relative integrated EQE (Int EQE) in the fullerene and polymer absorbing areas tracks to a large extent the exciton losses as calculated from the relative photoluminescence quenching (PLQ) efficiency after excitation of the fullerene and polymer.

Despite their outstanding photovoltaic performance, organic–inorganic perovskite solar cells still face severe stability issues and limitations in their device dimension. Further development of perovskite solar cells therefore requires a deeper understanding of loss mechanisms, in particular, concerning the origin and impact of trap states. Here, different surface properties of submicrometer sized CH₃NH₃PbI₃ particles are studied as a model system by photoluminescence spectroscopy to investigate the impact of the perovskite crystal surface on photoexcited states. Comparison of single crystals with either isolating or electron-rich surface passivation indicates the presence of positively charged surface trap states that can be passivated in case of the latter. These surface trap states cause enhanced nonradiative recombination at room temperature, which is a loss mechanism for solar cell performance. In the orthorhombic phase, the origin of multiple emission peaks is identified as the recombination of free and bound excitons, whose population ratio critically depends on trap state properties. The dynamics of exciton trapping at 50 K are observed on a time-scale of tens of picoseconds by a simultaneous population decrease and increase of free and bound excitons, respectively. These results emphasize the potential of surface passivation to further improve the performance of perovskite solar cells.

A comparison of electron-rich and isolating surface passivation of submicrometer sized CH₃NH₃PbI₃ single crystals reveals the presence of positively charged trap states at the crystal surface. Photoluminescence measurements at different temperatures demonstrate that these surface trap states cause surface lattice distortions and nonradiative recombination at room temperature and energy transfer from free excitons to bound excitons at low temperatures.

The p-type inorganic semiconductor CuGaO₂ as a hole-transporting layer (HTL) in perovskite solar cells (PSCs) provides higher carrier mobility, better-energy level matching, and superior stability, as well as low-temperature processing technique. Compared to organic HTL, a very competitive PCE of 18.51% with long-term stability is achieved. This indicates that CuGaO₂ is a promising HTL for efficient and stable PSCs.

Understanding the degradation mechanisms of organic photovoltaics is particularly important, as they tend to degrade faster than their inorganic counterparts, such as silicon and cadmium telluride. An overview is provided here of the main degradation mechanisms that researchers have identified so far that cause extrinsic degradation from oxygen and water, intrinsic degradation in the dark, and photo-induced burn-in. In addition, it provides methods for researchers to identify these mechanisms in new materials and device structures to screen them more quickly for promising long-term performance. These general strategies will likely be helpful in other photovoltaic technologies that suffer from insufficient stability, such as perovskite solar cells. Finally, the most promising lifetime results are highlighted and recommendations to improve long-term performance are made. To prevent degradation from oxygen and water for sufficiently long time periods, OPVs will likely need to be encapsulated by barrier materials with lower permeation rates of oxygen and water than typical flexible substrate materials. To improve stability at operating temperatures, materials will likely require glass transition temperatures above 100 °C. Methods to prevent photo-induced burn-in are least understood, but recent research indicates that using pure materials with dense and ordered film morphologies can reduce the burn-in effect.

Understanding the degradation mechanisms that reduce the long-term stability in organic photovoltaics is imperative. The present understanding of degradation mechanisms and the strategies researchers can use to identify them in new materials are reviewed. Some of the relevant materials properties that can be tuned to improve the long-term performance of organic photovoltaics are identified.

Triplet excitons form in quasi-2D hybrid inorganic–organic perovskites and diffuse over 100 nm before radiating with >11% photoluminescence quantum efficiency (PLQE) at low temperatures.