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

Wide Bandgap Polymer with Narrow Photon Harvesting in Visible Light Range Enables Efficient Semitransparent Organic Photovoltaics

Organic solar cells (OSCs) have gained a rapid development in the past two decades and the power conversion efficiency (PCE) of single-junction OSC has recently approached 20%. The novel materials and device engineering are two key factors of this evolution. In this review, the device engineering, including morphology characterization and optimization, device physics, flexible and large-area OSCs, and stability of OSCs are systematically summarized. In addition, the current challenges, problems and future developments are also discussed. 

https://link.springer.com/content/pdf/10.1007/s11426-022-1256-8.pdf

Recent progress in organic solar cells (Part II device engineering)

A multi-stage machine learning and molecular dynamics simulation-assisted pipeline is introduced for the time- and cost-efficient design and screening of small molecule acceptors for organic solar cells. 

Machine learning and molecular dynamics simulation-assisted evolutionary design and discovery pipeline to screen efficient small molecule acceptors for PTB7-Th-based organic solar cells with over 15% efficiency

Harnessing energy from the sun is attracting increasing attention as the traditional fossil-based energy sources are being depleted. Photovoltaics (PV) is now an established technology and the most promising method...

Recent Progress in Organic Solar Cells Based on Non-Fullerene Acceptors: Materials to Devices

How to manipulate the phase separation and molecular arrangement to meet the need of efficient charge generation and extraction remains a long-standing challenge in all-small-molecule organic solar cells (ASM-OSCs). Herein, a small molecule acceptor Y7 as a morphology modulator was incorporated into a B1:BO-4Cl matrix to fabricate ternary ASM-OSCs. Y7 possesses excellent compatibility with the acceptor BO-4Cl but poor compatibility with the donor B1. The two acceptors prefer to form an alloy-like structure in ternary blends due to their good compatibility, which is conducive to fine-tuning the molecular arrangement for facilitating charge extraction. The inferior compatibility originating from the strong intermolecular interaction between Y7 and B1 can provide a driving force to manipulate the phase separation between the donor and acceptor for gaining well-formed nanofibrous and bi-continuous interpenetrating networks, leading to efficient charge separation, transport and collection in ternary blends. The ternary ASM-OSCs with 10 wt% Y7 in acceptors achieve a top-ranked power conversion efficiency of 16.28% with a holistic improvement of short-circuit current density, open-circuit voltage and fill factor. This work opens a new avenue to optimize the morphology for further boosting the performance of OSCs.

Rational compatibility in a ternary matrix enables all-small-molecule organic solar cells with over 16% efficiency

Despite dihalogenation of terminals is an effective strategy to achieve efficient nonfullerene acceptors (NFAs)-based organic solar cells (OSCs), hetero-dihalogenated terminals are quite difficult to obtain. Here, we firstly synthesized two new hetero-dihalogenated terminals (FCl-IC and FBr-IC) with a pair of fluorine/chlorine or fluorine/bromine at one terminal and three NFAs (Y-BO-FCl, Y-BO-FBr, and Y-BO-ClBr) with three hetero-dihalogenated terminals (FCl-IC, FBr-IC, and ClBr-IC) in a general process for OSCs, respectively. Y-BO-FCl neat film presents slightly lower energy level in comparison with those of Y-BO-FBr and Y-BO-ClBr. We, for the first time, obtained the single crystals of hetero-dihalogenated NFAs. From Y-BO-ClBr single crystal to fluorinated acceptor single crystals, the crystal systems and the intermolecular packing motifs have been significantly improved. The crystallographic and theoretical analysis indicate that Y-BO-FCl exhibits the most planar molecular geometry, the smallest intermolecular packing distance and the largest π−π electronic coupling among these acceptors. Moreover, PM6:Y-BO-FCl blend films present more order face-on orientation crystallinity, more suitable fiber-like phase separation, higher and more balanced charge mobility, weaker charge recombination in comparison with those of PM6:Y-BO-FBr and PM6:Y-BO-ClBr. As a result, up to remarkable PCE of 17.52% with enhanced FF of ca. 78% was achieved in binary Y-BO-FCl:PM6 devices compared to that of PM6:Y-BO-FBr (16.47%) and PM6:Y-BO-ClBr (13.61%), which is the highest efficiency for the hetero-halogenated NFAs-based OSCs. Our investigations demonstrate that fluorine/chlorine hetero-dihalogenated terminal is a new and effective synergistic strategy to induce significant difference in single crystallography and achieve high-performance hetero-halogenated NFAs-based OSCs.

Non-fullerene acceptors with hetero-dihalogenated terminals induce significant difference in single crystallography and enable binary organic solar cells with 17.5% efficiency

Over 17.6% Efficiency Organic Photovoltaic Devices with Two Compatible Polymer Donors

Two-Pronged Effect of Warm Solution and Solvent-Vapor Annealing for Efficient and Stable All-Small-Molecule Organic Solar Cells

A two-dimensional electron-rich fused-ring moiety (ClBDSe) based on benzo[1,2-b:4,5-b']diselenophene is synthesized. Three copolymers (PBDT-Se, PBDSe-T, and PBDSe-Se) are obtained by manipulating the connection types and number of selenophene units on the conjugated main chains with two 2D fused-ring units and two different π-bridges, respectively. In comparison with PBDT-Se and PBDSe-Se, PBDSe-T with benzo[1,2-b:4,5-b']diselenophene unit and thiophene π-bridge exhibits the deepest HOMO energy level and the strongest crystallinity in neat films. The PBDSe-T:Y6 blend film exhibits the best absorption complementarity, the most distinctive face-on orientation with proper phase separation, the highest carrier mobilities, and the lowest charge recombination among three blend films. Finally, the PBDSe-T:Y6-based device delivers an impressive power conversion efficiency (PCE) of 14.50 %, which is higher than those of PBDT-Se:Y6 and PBDSe-Se:Y6. Moreover, a decent open-circuit voltage (Voc ) of 0.89 V with a remarkably small energy loss of 0.44 eV is achieved for PBDSe-T:Y6. The efficiency of 14.50 % is the highest value for selenophene-containing copolymer-based binary organic solar cells (OSCs). This study provides evidence that introduction of 2D-benzo[1,2-b:4,5-b']diselenophene as a fused electron-rich unit with π-bridging into copolymeric donors is a valid strategy for providing high Voc and excellent PCE simultaneously in selenophene-based OSCs.

Two-Dimensional Conjugated Benzo[1,2-b:4,5-b']diselenophene-Based Copolymer Donor Enables Large Open-Circuit Voltage and High Efficiency in Selenophene-based Organic Solar Cells.

Mengyun Jiang

Papers

Rational compatibility in a ternary matrix enables all-small-molecule organic solar cells with over 16% efficiency

Non-fullerene acceptors with hetero-dihalogenated terminals induce significant difference in single crystallography and enable binary organic solar cells with 17.5% efficiency

Over 17.6% Efficiency Organic Photovoltaic Devices with Two Compatible Polymer Donors

Two-Pronged Effect of Warm Solution and Solvent-Vapor Annealing for Efficient and Stable All-Small-Molecule Organic Solar Cells

Two-Dimensional Conjugated Benzo[1,2-b:4,5-b']diselenophene-Based Copolymer Donor Enables Large Open-Circuit Voltage and High Efficiency in Selenophene-based Organic Solar Cells.