ZiQi Sun

Periodic nanocone-nanopillar dual-structured arrays are wet chemical etched on 20 μm-thick crystalline silicon substrates by Pingqi Gao, Xiaofeng Li, Jichun Ye and co-workers in article number 1501793. This structure enables the realization of excellent light absorption properties and enhanced electrical contact with PEDOT:PSS. The final textured silicon/PEDOT:PSS thin film hybrid solar cell shows a power conversion efficiency of 12.2%.

A kesterite Cu₂ZnSnS₄ thin film solar cell with efficiency of over 9% is obtained by utilizing Zn_1–xCd_xS film as a replacement to traditional CdS buffer layer. Zn_1–xCd_xS film can optimize the conduction band offset between Cu₂ZnSnS₄ absorber and buffer, forming a minor positive conduction band alignment, thereby alleviating the recombination significantly and improving the open circuit voltage and fill factor efficiently.

For realizing flexible perovskite solar cells (PSCs), it is important to develop low-temperature processable interlayer materials with excellent charge transporting properties. Herein, a novel polymeric hole-transport material based on 1,4-bis(4-sulfonatobutoxy)benzene and thiophene moieties (PhNa-1T) and its application as a hole-transport layer (HTL) material of high-performance inverted-type flexible PSCs are introduced. Compared with the conventionally used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the incorporation of PhNa-1T into HTL of the PSC device is demonstrated to be more effective for improving charge extraction from the perovskite absorber to the HTL and suppressing charge recombination in the bulk perovskite and HTL/perovskite interface. As a result, the flexible PSC using PhNa-1T achieves high photovoltaic performances with an impressive power conversion efficiency of 14.7%. This is, to the best of our knowledge, among the highest performances reported to date for inverted-type flexible PSCs. Moreover, the PhNa-1T-based flexible PSC shows much improved stability under an ambient condition than PEDOT:PSS-based PSC. It is believed that PhNa-1T is a promising candidate as an HTL material for high-performance flexible PSCs.

By incorporating low-temperature solution-processable 1,4-bis(4-sulfonatobutoxy)benzene and thiophene moieties polymer as a hole-transport layer, highly efficient, environmental stable, and mechanically flexible planar-heterojunction perovskite solar cell has been successfully achieved with an excellent power conversion efficiency of 14.7%.

On page 2426, C. P. Grigoropoulos, S. Kim, Y. K. Hong, and co-workers demonstrate a novel process architecture for flexible electronics. The multilayer molybdenum disulfide thin-film transistor array fabricated according to this scheme exhibits not only outstanding device performances, but also no apparent degradation under various mechanical stresses. These results could provide important applications in the fabrication of flexible integrated circuitry for various versatile functions.

Formamidinium lead iodide (FAPbI₃) has a broader absorption spectrum and better thermal stability than the most famous methylammonium lead iodide, thus exhibiting great potential for photovoltaic applications. In this report, the light-induced photoluminescence (PL) evolution in FAPbI₃ thin films is investigated. The PL intensity evolution is found to be strongly dependent on the atmosphere surrounding the samples. When the film is exposed to air, its photoluminescence intensity is enhanced more than 140 times after continuous ultraviolet laser illumination for 2 h, and the average lifetime is prolonged from 17 to 389 ns. The enhanced photoluminescence implies that the trap density is significantly reduced. The comparative study of the photoluminescence properties in air, nitrogen, and oxygen/helium environment suggests that moisture is important for the PL enhancement. This is explained in terms of moisture-assisted light-healing effect in FAPbI₃ thin films. With this study, a new method is demonstrated to increase and control the quality of hybrid perovskite thin films.

Laser healing perovskites: Photophysical properties of FAPbI₃ thin films under continuous UV illumination are investigated. Giant light-induced enhancement of the photoluminescence intensity is observed when the sample is exposed to air. It is demonstrated that moisture plays a critical role in the light-induced photoluminescence enhancement effect. Laser healing in air can become a way to improve the quality of perovskite thin films.

A photoconductor based on composite conductive polymer nanowires embedded with one-dimensional gold nanoparticle chains is developed by L. Jiang, X. Chen, and co-workers, as shown on page 2978. The precise and controllable positioning of the nanoparticle array in the composite photoconductor endues a distinct plasmon-resonance-coupling effect, which plays a critical role in promoting and modulating the photoresponse behavior by the excitation-light wavelength or the power.

Solution-processed organic solar cells are promising owing to their light weight, ease of processability, low cost, flexibility, and large-area fabrication. Particularly, small-molecule active materials have been recently developed using straightforward synthesizing methods, exhibiting the least batch-to-batch variation in physical and optoelectronic properties and highly reproducible efficiency. A series of 2D-BDT-based active materials with various numbers of benzodithiophene (BDT) units and how the number of 2D-BDT units influences the construction of a well-defined interconnected structure are reported. The systematically controlled morphology of the 2D-BDT material helps achieve a high power-conversion efficiency (PCE) of 8.56% and a high fill factor of 0.73 without the use of additives. The reduced charge recombination and well-constructed morphology of this material facilitate a PCE of 7.45% in a 77.8 cm² rigid module, which is the outstanding performance in large-area modules.

The delicate control of intermolecular interaction has an important role in achieving well-interconnected bulk heterojunctions (BHJ). It is demonstrated that the number of 2D-BDT units is essential in creating a well-defined intermolecular interaction and the desired interconnected BHJ. High efficiency of 8.56% in small area, and 7.45% in a 77.8 cm² rigid module is achieved.

Copper has attracted significant interests as an abundant and low-cost alternative material for flexible transparent conducting electrodes (FTCEs). However, Cu-based FTCEs still present unsolved technical issues, such as their inferior light transmittance and oxidation durability compared to conventional indium tin oxide (ITO) and silver metal electrodes. This study reports a novel technique for fabricating highly efficient FTCEs composed of a copper ultrathin film sandwiched between zinc oxides, with enhanced transparency and antioxidation performances. A completely continuous and smooth copper ultrathin film is fabricated by a simple room-temperature reactive sputtering process involving controlled nitrogen doping (<1%) due to a dramatic improvement in the wettability of copper on zinc oxide surfaces. The electrode based on the nitrogen-doped copper film exhibits an optimized average transmittance of 84% over a spectral range of 380 −1000 nm and a sheet resistance lower than 20 Ω sq⁻¹, with no electrical degradation after exposure to strong oxidation conditions for 760 h. Remarkably, a flexible organic solar cell based on the present Cu-based FTCE achieves a power conversion efficiency of 7.1%, clearly exceeding that (6.6%) of solar cells utilizing the conventional ITO film, and this excellent performance is maintained even in almost completely bent configurations.

A highly stable, flexible, conductive, and transparent electrode based on a completely continuous, smooth nitrogen-doped ultrathin Cu film is developed by an innovative room-temperature reactive sputtering process. The electrode is employed to fabricate highly efficient bendable organic solar cells built on polymer substrates.

The efficiencies of a number of electrochemical devices (e.g., fuel cells and metal-air batteries) are mainly governed by the kinetics of the oxygen reduction reaction (ORR). Among all the good ORR catalysts, the partially substituted double perovskite oxide (AA′B₂O_5+δ) has the unique layered structure, providing a great flexibility regarding the optimization of its electronic structures and physicochemical properties. Here, it is demonstrated that the double perovskite oxide, i.e., NdBa_0.75Ca_0.25Co_1.5Fe_0.5O_5+δ, is a good ORR catalyst at both room and elevated temperatures. Under ambient condition, its half-wave potential of ORR in alkaline media is as low as 0.74 V versus RHE; at 650 °C, the cathodic polarization resistance is merely 0.0276 Ω cm² according to a symmetric cell measurement, whereas the solid oxide fuel cells using this cathode exhibit a maximum power density of 1982 mW cm⁻². From various materials characterizations, it is hypothesized that its excellent ORR activity is strongly correlated with the crystallographic, electronic, and defect structures of the materials.

The double perovskite oxide, i.e., NdBa_0.75Ca_0.25Co_1.5Fe_0.5O_5+δ, is demonstrated to be a good oxygen reduction reaction (ORR) catalyst at both room and elevated temperatures, and we also hypothesize that the excellent ORR activity strongly correlates to the crystallographic, electronic, and the defect structures of the material.

Organic–inorganic lead halide perovskites are emerging materials for the next-generation photovoltaics. Lead halides are the most commonly used lead precursors for perovskite active layers. Recently, lead acetate (Pb(Ac)₂) has shown its superiority as the potential replacement for traditional lead halides. Here, we demonstrate a strategy to improve the efficiency for the perovskite solar cell based on lead acetate precursor. We utilized methylammonium bromide as an additive in the Pb(Ac)₂ and methylammonium iodide precursor solution, resulting in uniform, compact and pinhole-free perovskite films. We observed enhanced charge carrier extraction between the perovskite layer and charge collection layers and delivered a champion power conversion efficiency of 18.3% with a stabilized output efficiency of 17.6% at the maximum power point. The optimized devices also exhibited negligible current density–voltage (J–V) hysteresis under the scanning conditions.

High-performance inverted perovskite solar cells based on lead acetate precursor are demonstrated with power conversion efficiency exceeding 18% and stabilized output efficiency of 17.6%. Methylammonium bromide was utilized as additive into the lead acetate precursor solutions, leading to the perovskite films with improved performance.

A new n-type polymer, PF3N-2TNDI, with high electron mobility, is developed as efficient cathode interfacial material and interconnecting layer (ICL) for constructing high-performance tandem organic solar cells. Tandem cells employing the ICL with structure of PF3N-2TNDI/Ag/PEDOT:PSS achieve a high power conversion efficiency (PCE) of 11.35%. Moreover, flexible tandem cells with PCE over 10% are also demonstrated.

A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.

A new category of deep-absorbing small molecules is developed. Optimized devices driven by mixed additives show a remarkable short-circuit current of ≈20 mA cm⁻² and a highest power conversion efficiency of 9.06%. A multi-length-scale morphology is formed, which is fully characterized by resonant soft X-ray scattering, high-angle annular dark film image transmission electron microscopy, etc.

A series of star-shaped small molecular cathode interlayer materials are synthesized for PTB7:PC₇₁BM based polymer solar cells (PSCs), comprising neutral amino groups, quaternary ammonium ions, amino N-oxides, and sulfobetaine ions as pendant polar functionalities, respectively. For the first time, the effect of these different pendant functional groups with or without mobile counterions on the cells' photovoltaic properties is investigated in detail. A large improvement in device performance is observed by inserting these cathode interfacial layers (CILs) between the PTB7:PC₇₁BM active layer and the Al electrode. The CILs could effectively lower the work function of the Al cathode, increase the built-in potential, and decrease the series resistance of the related PSCs. poly(9,9-dioctylfluorene-co-N-[4-(3-methyl-propyl)]-diphenylamine) with pendant quaternary ammonium ions shows the best cathode modification ability, giving rise to the highest power conversion efficiency of 10.1%, even better than that of the typical poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] based device. The design strategy and structure–property relationships concluded in this work will be helpful to develop more efficient cathode interface materials for high-performance PSCs in the future.

A series of star-shaped small molecular cathode interlayer materials with variable pendant polar functionalities are designed for polymer solar cells. For the first time, the effect of different pendant functional groups with/without mobile counterions on the cell's photovoltaic properties is investigated. Poly(9,9-dioctylfluorene-co-N-[4-(3-methyl-propyl)]-diphenylamine) with pendant quaternary ammonium ions (TFB) shows the best cathode modification capability, achieving an efficiency of 10.1%.

In article number 1502206, Aleksandra B. Djurišić and co-workers discuss whether excess PbI₂ is beneficial for perovskite solar cell performance. The presence of unreacted PbI₂ is commonly believed to be beneficial to the efficiency of perovskite solar cells. However, it results in an intrinsic instability of the illuminated film even in inert atmosphere, leading to accelerated film degradation under illumination.

In article number 1502027, Dehong Chen, Yi-Bing Cheng, Rachel A. Caruso and co-workers demonstrate the structural tuning of titania, producing films of nanoparticles, nanowires or nanosheets for perovskite solar cells. The porous network and fast electron transfer of the nanowire and nanosheet thin films enable perovskite infiltration, facilitate charge extraction and suppress charge recombination.

In organic donor–acceptor systems, ultrafast interfacial charge transfer (CT), charge separation (CS), and charge recombination (CR) are key determinants of the overall performance of photovoltaic devices. However, a profound understanding of these photophysical processes at device interfaces remains superficial, creating a major bottleneck that circumvents advancements and the optimization of these solar cells. Here, results from time-resolved laser spectroscopy and high-resolution electron microscopy are examined to provide the fundamental information necessary to fabricate and optimize organic solar cell devices. In real time, CT and CS are monitored at the interface between three fullerene acceptors (FAs) (PC₇₁BM, PC₆₁BM, and IC₆₀BA) and the PTB7-Th donor polymer. Femtosecond transient absorption (fs-TA) data demonstrates that photoinduced electron transfer from the PTB7-Th polymer to each FA occurs on the sub-picosecond time scale, leading to the formation of long-lived radical ions. It is also found that the power conversion efficiency improves from 2% in IC₆₀BA-based solar cells to >9% in PC₇₁BM-based devices, in support of our time-resolved results. The insights reported in this manuscript provide a clear understanding of the key variables involved at the device interface, paving the way for the exploitation of efficient CS and subsequently improving the photoconversion efficiency.

A complete understanding of the charge transfer, charge separation, and charge recombination at D/A interfaces is integral for boosting solar cell photoconversion efficiency (PCE). Time-resolved laser spectroscopy and high-resolution electron microscopy provide a basis for accomplishing the high performance solar cell. The device optimization enhanced the PCE from 2% in IC₆₀BA-based to >9% in PC₇₁BM-based solar cells.

High efficiency and air stable doctor-blade coated perovskite solar cells are reported. The high quality mixed cation perovskite film (FA _x MA_{1− x} PbI₃) is fabricated by taking the unique advantage of doctor-blade coating method, based on which solar cell efficiency larger than 18% is realized. In addition, choosing copper as cathode enhances device environmental stability substantially, paving the way for real applications.

The latest advances in colloidal-quantum-dot material processing are combined with a double-sided junction architecture, which is done by efficiently incorporating indium ions in the ZnO eletrode. This platform allows the collection of all photogenerated carriers even at the maximum power point. The increased depletion width in the device facilitates full carrier collection, leading to a record 10.8% power conversion efficiency.