Key Takeaways & Executive Findings
- •• Dual-donor strategy with PTzBI-dF enhances crystallinity, achieving 19.23% efficiency in organic solar cells. • PTzBI-dF suppresses trap-assisted recombination and current leakage, improving device stability (82% PCE retention after 800 h). • The approach is versatile, boosting PCE by >1% across various Y6 derivatives. • Donor phase engineering offers a practical route to optimize molecular packing for high-performance OSCs.
Abstract
Trap-assisted charge recombination is one of the primary limitations of restricting the performance of organic solar cells. However, effectively reducing the presence of traps in the photoactive layer remains challenging. Herein, wide bandgap polymer donor PTzBI-dF is demonstrated as an effective modulator for enhancing the crystallinity of the bulk heterojunction active layers composed of D18 derivatives blended with Y6, leading to dense and ordered molecular packings, and thus, improves photoluminescence quenching properties. As a result, the photovoltaic devices exhibit reduced trap-assisted charge recombination losses, achieving an optimized power conversion efficiency of over 19%. Besides the efficiency enhancement, the devices comprised of PTzBI-dF as a third component simultaneously attain decreased current leakage, improved charge carrier mobilities, and suppressed bimolecular charge recombination, leading to reduced energy losses. The advanced crystalline structures induced by PTzBI-dF and its characteristics, such as well-aligned energy level, and complementary absorption spectra, are ascribed to the promising performance improvements. Our findings suggest that donor phase engineering is a feasible approach to tuning the molecular packings in the active layer, providing guidelines for designing effective morphology modulators for high-performance organic solar cells.
1. Introduction
Organic solar cells (OSCs) attract broad research interests due to their properties, such as portability, flexibility, and printability [1–9]. Owing to the development of nonfullerene acceptors (NFAs), for instance, Y6 and its derivatives, the power conversion efficiency (PCE) of both single-junction OSCs and tandem devices has exceeded 20% [10, 11]. Besides the chemical structures of the donor or acceptor materials, the nongeminate recombination losses, especially trap-assisted charge recombination, are the primary limiting factors to improving the PCE of OSCs further. Therefore, reducing nongeminate recombination is a practical approach to enhance the performance of OSCs. To this end, optimizing methods, such as the selection of solvents, the regulation of additives, the introduction of a third component, interface engineering, and various post-treatment methods, were applied [12–20].
Adding a third component is demonstrated as one feasible way to broaden the absorption spectra, regulate the energy level, improve the crystallinity/phase separation, and increase the charge transport and transfer properties, potentially inhibiting the free charge recombination for enhancing the photovoltaic performance of OSCs [21–28]. A small NFA, m-BTP-PhC6, was used to regulate the active layer morphology as a second acceptor. Due to the good compatibility between m-BTP-PhC6 and D18-Cl: Y6 blend and the matching quasi cascade energy level arrangement, the exciton separation efficiency was improved, and the trap-assisted charge recombination loss was effectively reduced, leading to improved devices’ performance [29]. Besides introducing NFAs as the third component, dual donors with good miscibility were usually used for efficient ternary OSCs [30–32]. A polymer donor S3 with 20% chlorinated thiophene units was synthesized and added to PM6:Y6 as the third component. The dual donors formed an alloy-like thin film due to their excellent compatibility, resulting in enhanced charge generation and extraction, and finally achieved a PCE of 17.53% [33]. When D18-Cl was added to PM6:L8-BO, an alloy morphology was formed due to
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Anhai Liang, Yuqing Sun, Sein Chung, Jiyeong Shin, Kangbo Sun, Chaofeng Zhu, Jingjing Zhao, Zhenmin Zhao, Yufei Zhong, Guangye Zhang, Kilwon Cho, Zhipeng Kan (2024). Dual-Donor-Induced Crystallinity Modulation Enables 19.23% Efficiency Organic Solar Cells. Nano-Micro Letters. https://doi.org/10.1007/s40820-024-01576-1
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Frequently Asked Questions
What is the main achievement of this study?
The study demonstrates a dual-donor strategy using PTzBI-dF to modulate crystallinity, achieving a power conversion efficiency of 19.23% in organic solar cells.
How does PTzBI-dF improve device performance?
PTzBI-dF enhances crystallinity, reduces trap-assisted recombination, decreases current leakage, and improves charge carrier mobilities, leading to higher efficiency and stability.
What is the stability of the optimized devices?
The ternary devices retain 82% of their initial PCE after 800 hours of illumination, indicating improved operational stability.
Is the dual-donor strategy applicable to other material systems?
Yes, the strategy is applicable to various Y6 derivatives, with PCE improvements exceeding 1% in different systems.
What is the significance of donor phase engineering?
Donor phase engineering provides a feasible approach to tune molecular packing in the active layer, offering guidelines for designing effective morphology modulators for high-performance organic solar cells.
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