Constructing CdS-Based Electron Transporting Layers With Efficient Electron Extraction for Perovskite Solar Cells
Cheng Luo, Ping Jiang, Liusen Hu, Moran Bian, Lei Wan, Haihong Niu, Xiaoli Mao, Ru Zhou, Jun Xu
Abstract
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 (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , ZnO, SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , 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 CdCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (c-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) 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-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> PbI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> PSC based on the bilayer c-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /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%.