It is essential to minimize the interfacial trap states and improve the carrier collection for high efficiency perovskite solar cells (PSCs). Herein, we present a facile method to construct a p‐type graded heterojunction (GHJ) in normal PSCs by deploying a gradient distribution of hole‐transporting materials (poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine], PTAA, in this case) in the shallow perovskite layer. The formation of the GHJ structure facilitates charge transfer and collection, and passivates interfacial trap states, thus delivering a power conversion efficiency (PCE) of 20.05 % along with steady output efficiency of 19.3 %, which is among the highest efficiencies for cesium formamidinium (Cs–FA) lead halide PSCs. Moreover, the unencapsulated devices based on these (Cs–FA) lead halide perovskites show excellent long‐term stability; more than 95 % of their initial PCE can be retained after 1440 h storage under ambient conditions. This study may provide an effective strategy to fabricate high‐efficiency PSCs with great stability.

中文翻译：

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高效铯二甲铵双阳离子卤化钙钛矿型太阳能电池的异质结工程

对于高效钙钛矿太阳能电池（PSC），必须最小化界面陷阱状态并改善载流子收集。本文中，我们提出了一种通过部署空穴传输材料（聚[双（4-苯基）（2,4,6-三甲基苯基）胺）的梯度分布在普通PSC中构建ap型渐变异质结（GHJ）的简便方法。 （在这种情况下为PTAA）在浅钙钛矿层中。GHJ结构的形成有利于电荷转移和收集，并钝化界面陷阱态，因此提供20.05％的功率转换效率（PCE）和19.3％的稳定输出效率，这是铯form（Cs）的最高效率之一–FA）卤化铅PSC。此外，基于这些（Cs–FA）卤化钙铅钙钛矿的未封装器件具有出色的长期稳定性。在环境条件下储存1440小时后，可以保留超过95％的初始PCE。这项研究可能为制造高稳定性的高效PSC提供了有效的策略。