A record power conversion efficiency (PCE) of over 19% is realized in planar‐mixed heterojunction (PMHJ) organic solar cells (OSCs) by adopting the asymmetric selenium substitution strategy in making a pseudosymmetric electron acceptor, BS3TSe‐4F. The combined molecular asymmetry with more polarizable selenium substitution increases the dielectric constant of the D18/BS3TSe‐4F blend, helping lower the exciton binding energy. On the other hand, dimer packing in BS3TSe‐4F is facilitated to enable free charge generation, helping more efficient exciton dissociation and lowering the radiative recombination loss (ΔE2) of OSCs. As a result, PMHJ OSCs based on D18/BS3TSe‐4F achieve a PCE of 18.48%. By incorporating another mid‐bandgap acceptor Y6‐O into D18/BS3TSe‐4F to form a ternary PMHJ, a higher open‐circuit voltage (VOC) can be achieved to realize an impressive PCE of 19.03%. The findings of using pseudosymmetric electron acceptors in enhancing device efficiency provides an effective way to develop highly efficient acceptor materials for OSCs.

Achieving 19% Power Conversion Efficiency in Planar‐Mixed Heterojunction Organic Solar Cells Using a Pseudosymmetric Electron Acceptor

The development of polymerized small‐molecule acceptors has boosted the power conversion efficiencies (PCEs) of all‐polymer organic photovoltaic (OPV) cells to 17%. However, the polymer donors suitable for all‐polymer OPV cells are still lacking, restricting the further improvement of their PCEs. Herein, a new polymer donor named PQM‐Cl is designed and its photovoltaic performance is explored. The negative electrostatic potential and low average local ionization energy distribution of the PQM‐Cl surface enable efficient charge generation and transfer process. When blending with a well‐used polymer acceptor, PY‐IT, the PQM‐Cl‐based devices deliver an impressive PCE of 18.0% with a superior fill factor of 80.7%, both of which are the highest values for all‐polymer OPV cells. The relevant measurements demonstrate that PQM‐Cl‐based films possess excellent mechanical and flexible properties. As such, PQM‐Cl‐based flexible photovoltaic cells are fabricated and an excellent PCE of 16.5% with high mechanical stability is displayed. These results demonstrate that PQM‐Cl is a potential candidate for all‐polymer OPV cells and provide insights into the design of polymer donors for high‐efficient all‐polymer OPV cells.

A New Polymer Donor Enables Binary All‐Polymer Organic Photovoltaic Cells with 18% Efficiency and Excellent Mechanical Robustness

Since their introduction over two decades ago, nanostructured soft magnetic alloys have demonstrated excellent magnetic softness and improved performance over a wide range of environmental conditions. This chapter gives an updated account of progress in alloy design, synthesis, structure, and performance of this class of alloys. Existing data are reviewed to highlight recent advances and promote new perspectives for future work in this area.

Nanocrystalline Soft Magnetic Alloys Two Decades of Progress

High-Efficiency Ternary Organic Solar Cells with a Good Figure-of-Merit Enabled by Two Low-Cost Donor Polymers

Hole‐transporting layers (HTLs) are an essential component in inverted, p–i–n perovskite solar cells (PSCs) where they play a decisive role in extraction and transport of holes, surface passivation, perovskite crystallization, device stability, and cost. Currently, the exploration of efficient, stable, highly transparent and low‐cost HTLs is of vital importance for propelling p–i–n PSCs toward commercialization. Compared to their inorganic counterparts, organic HTLs offer multiple advantages such as a tunable bandgap and energy level, easy synthesis and purification, solution processability, and overall low cost. Here, recent progress of organic HTLs, including conductive polymers, small molecules, and self‐assembled monolayers, as utilized in inverted PSCs is systematically reviewed and summarized. Their molecular structure, hole‐transport properties, energy levels, and relevant device properties and resulting performances are presented and analyzed. A summary of design principles and a future outlook toward highly efficient organic HTLs in inverted PSCs is proposed. This review aims to inspire further innovative development of novel organic HTLs for more efficient, stable, and scalable inverted PSCs.

Organic Hole‐Transport Layers for Efficient, Stable, and Scalable Inverted Perovskite Solar Cells

Achieving high efficiency and well-kept ductility in ternary all-polymer organic photovoltaic blends thanks to two well miscible donors

Monolithic perovskite/organic tandem solar cells with 23.6% efficiency enabled by reduced voltage losses and optimized interconnecting layer

Abstract Rationally utilizing and developing synthetic units is of particular significance for the design of high-performance non-fullerene small-molecule acceptors (SMAs). Here, a thieno[3,2-b]pyrrole synthetic unit was employed to develop a set of SMAs (ThPy1, ThPy2, ThPy3 and ThPy4) by changing the number or the position of the pyrrole ring in the central core based on a standard SMA of IT-4Cl, compared to which the four thieno[3,2-b]pyrrole-based acceptors exhibit bathochromic absorption and upshifted frontier orbital energy level due to the strong electron-donating ability of pyrrole. As a result, the polymer solar cells (PSCs) of the four thieno[3,2-b]pyrrole-based acceptors yield higher open-circuit voltage and lower energy loss relative to those of the IT-4Cl-based device. What is more, the ThPy3-based device achieves a power conversion efficiency (PCE) (15.3%) and an outstanding fill factor (FF) (0.771) that are superior to the IT-4Cl-based device (PCE = 12.6%, FF = 0.758). The ThPy4-based device realizes the lowest energy loss and the smallest optical band gap, and the ternary PSC device based on PM6:BTP-eC9:ThPy4 exhibits a PCE of 18.43% and a FF of 0.802. Overall, this work sheds light on the great potential of thieno[3,2-b]pyrrole-based SMAs in realizing low energy loss and high PCE.

Ru-Zhang Ma

Papers

Achieving high efficiency and well-kept ductility in ternary all-polymer organic photovoltaic blends thanks to two well miscible donors

Monolithic perovskite/organic tandem solar cells with 23.6% efficiency enabled by reduced voltage losses and optimized interconnecting layer

Monolithic perovskite/organic tandem solar cells with 23.6% efficiency enabled by reduced voltage losses and optimized interconnecting layer

High-Efficiency Ternary Organic Solar Cells with a Good Figure-of-Merit Enabled by Two Low-Cost Donor Polymers

Heteroheptacene-based acceptors with thieno[3,2-b]pyrrole yield high-performance polymer solar cells