Liuyanfeng

On page 3366, P. M. Beaujuge and co-workers describe homo-tandem solar cells constructed by stacking identical subcells solution-processed from blends of the wide-bandgap polymer donor PBDTTPD and the fullerene acceptor PCBM, which achieve power conversion efficiencies >8% and open-circuit voltages >1.8 V. The homo-tandem devices provide sufficient voltage to induce the dissociation of water in an electrochemical cell. The authors acknowledge Hyun Ho Hwang (Heno) for developing the artwork.

Highly efficient polymer solar cells with tandem structure are fabricated by using two excellent photovoltaic polymers and a highly transparent intermediate recombination layer. Power conversion efficiencies over 11% can be realized featured by a low-band-gap polymer with fine-tuned properties.

A novel donor–acceptor type conjugated polymer based on a building block of 4,8-di(thien-2-yl)-6-octyl-2-octyl-5H-pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione (TZBI) as the acceptor unit and 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)­benzo­[1,2-b:4,5-b′]dithiophene as the donor unit, named as PTZBIBDT, is developed and used as an electron-donating material in bulk-heterojunction polymer solar cells. The resulting copolymer exhibits a wide bandgap of 1.81 eV along with relatively deep highest occupied molecular orbital energy level of −5.34 eV. Based on the optimized processing conditions, including thermal annealing, and the use of a water/alcohol cathode interlayer, the single-junction polymer solar cell based on PTZBIBDT:PC₇₁BM ([6,6]-phenyl-C₇₁-butyric acid methyl ester) blend film affords a power conversion efficiency of 8.63% with an open-circuit voltage of 0.87 V, a short circuit current of 13.50 mA cm⁻², and a fill factor of 73.95%, which is among the highest values reported for wide-bandgap polymers-based single-junction organic solar cells. The morphology studies on the PTZBIBDT:PC₇₁BM blend film indicate that a fibrillar network can be formed and the extent of phase separation can be mani­pulated by thermal annealing. These results indicate that the TZBI unit is a very promising building block for the synthesis of wide-bandgap polymers for high-performance single-junction and tandem (or multijunction) organic solar cells.

A novel electron-accepting cyclic-imide substituted benzotriazole unit TZBI (4,8-di(thien-2-yl)-6-octyl-2-octyl-5H-pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione) is developed, which can pair with benzo[1,2-b:4,5-b′]dithiophene to present a donor–acceptor wide-bandgap conjugated polymer. High-performance polymer solar cell with a champion power conversion efficiency of 8.63% is realized, demonstrating that TZBI can be a very promising building block for wide-bandgap conjugated polymers.

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.

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%.

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.

In article number 1500392, Z. Liang and co-workers review the development of structure and growth control of organic–inorganic halide perovskites for optoelectronics, in the forms of polycrystalline films and single crystals ranging from three, two, one, and zero dimensions, ideal platforms for fundamental studies due to the absence of grain boundaries.

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.

A novel fullerene cathode interlayer is employed to facilitate the fabrication of stable and efficient perovskite solar cells. This modified fullerene surfactant significantly increases air stability of the derived devices due to its hydrophobic characteristics to enable 80% of the initial PCE to be retained after being exposed in ambient condition with 20% relative humidity for 14 days.