Trap-induced nonradiative recombination and decomposition are the major limiting factors that hinder the development of mixed-halide wide-bandgap perovskite solar cells. Specifically, the incorporation of formamidinium (FA⁺) and bromide in wide-bandgap (WBG) perovskite materials leads to shallow-energy-level traps and inferior light stability. Herein, the electron-withdrawing molecule 2,3,5,6 tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) is used as an effective passivator and stabilizer, which has molecular interaction with the FA⁺ cation for reducing trap densities and enhancing the stability of WBG perovskite solar cells. It is found that the extended π aromatic system in F4-TCNQ can enhance the binding energy and stabilize the FA⁺ cation in perovskite films. Furthermore, the 1.67 eV bandgap inverted perovskite solar cells with a small amount of F4-TCNQ have shallower defect levels, reduced trap density, and decreased nonradiative recombination, therefore giving a remarkably improved power conversion efficiency (PCE) of 20.0%. Most importantly, the unencapsulated devices with F4-TCNQ additive have greatly enhanced stability, maintaining 88% of their peak PCEs under continuous illumination after 840 h, whereas the control devices only retain 48% of their PCEs after 500 h.

中文翻译：

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揭示π芳香分子作为高效宽禁带钙钛矿太阳能电池有效钝化剂和稳定剂的机制

陷阱诱导的非辐射复合和分解是阻碍混合卤化物宽带隙钙钛矿太阳能电池发展的主要限制因素。具体而言，在宽带隙（WBG）钙钛矿材料中加入甲脒（FA ⁺）和溴化物会导致浅能级陷阱和较差的光稳定性。在此，吸电子分子 2,3,5,6 四氟-7,7,8,8-四氰基醌二甲烷 (F4-TCNQ) 用作有效的钝化剂和稳定剂，它与 FA ⁺阳离子具有分子相互作用以减少陷阱密度并提高 WBG 钙钛矿太阳能电池的稳定性。发现 F4-TCNQ 中扩展的 π 芳香体系可以提高结合能并稳定 FA ⁺钙钛矿薄膜中的阳离子。此外，具有少量 F4-TCNQ 的 1.67 eV 带隙倒置钙钛矿太阳能电池具有更浅的缺陷水平、更低的陷阱密度和更低的非辐射复合，因此显着提高了 20.0% 的功率转换效率 (PCE)。最重要的是，带有 F4-TCNQ 添加剂的未封装器件的稳定性大大提高，在 840 小时后连续照明下保持其峰值 PCE 的 88%，而控制器件在 500 小时后仅保留其 PCE 的 48%。