The electron transporting layer (ETL) is a critical component in perovskite solar cells (PSCs) and plays an important role in extracting and transporting electrons. However, the commonly used wide-bandgap metal oxides (TiO2, ZnO, SnO2, etc.) often involve undesirable photocatalytic activity towards perovskite materials under UV light, which would undermine the long-term stability of PSCs. In this article, nonoxide CdS ultra-thin films were deposited onto conducting substrates through chemical bath deposition to serve as ETLs. It is revealed that the subsequent CdCl2 treatment followed by annealing is not essential to CdS ETLs for PSCs; this fact is quite different from the scenario demonstrated for conventional thin-film solar cells. Moreover, a compact TiO2 (c-TiO2) blocking layer was introduced between the conducting substrate and the CdS layer to further enhance the electron extraction capability of ETLs and boost the photovoltaic performance of PSCs. Through careful morphology, optical and electrical characterizations, it is found that the presence of the c-TiO2 underlayer avoids the partially exposure of substrate bumps, enlarges the subsequently deposited perovskite crystals, forms cascade energy level alignments, and accelerates the electron extraction from perovskite to ETLs. Therefore, the shunt current leakage and the charge recombination at the ETL/perovskite interface are significantly suppressed. Eventually, the CH3NH3PbI3 PSC based on the bilayer c-TiO2/CdS ETL yields a promising power conversion efficiency of 15.11%, which is much higher than that of the single-layer CdS-based device. This work delivers one of the few CdS ETL-based PSCs that exhibit efficiencies over 15%.

中文翻译：

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为钙钛矿太阳能电池构建具有高效电子提取的 CdS 基电子传输层


电子传输层（ETL）是钙钛矿太阳能电池（PSC）的关键组成部分，在提取和传输电子方面发挥着重要作用。然而，常用的宽带隙金属氧化物（TiO2、ZnO、SnO2等）在紫外光下通常会对钙钛矿材料产生不良的光催化活性，这会破坏PSC的长期稳定性。在本文中，通过化学浴沉积将非氧化物 CdS 超薄膜沉积到导电基底上，用作 ETL。结果表明，随后的 CdCl2 处理和退火对于 PSC 的 CdS ETL 来说并不是必需的；这一事实与传统薄膜太阳能电池所展示的情况截然不同。此外，在导电基底和CdS层之间引入致密的TiO2（c-TiO2）阻挡层，以进一步增强ETL的电子提取能力并提高PSC的光伏性能。通过仔细的形貌、光学和电学表征，发现c-TiO2底层的存在避免了基板凸块的部分暴露，扩大了随后沉积的钙钛矿晶体，形成级联能级排列，并加速了电子从钙钛矿中提取到ETL。因此，ETL/钙钛矿界面处的分流电流泄漏和电荷复合被显着抑制。最终，基于双层c-TiO2/CdS ETL的CH3NH3PbI3 PSC的功率转换效率高达15.11%，远高于单层CdS器件。这项工作提供了少数几个基于 CdS ETL 的 PSC 之一，其效率超过 15%。