Both the film quality and the electronic properties of halide perovskites have significant influences on the photovoltaic performance of perovskite solar cells (PSCs) because both of them are closely related to the charge carrier transportation, separation, and recombination processes in PSCs. In this work, an additive engineering strategy using antimony acetate (Sb(Ac) 3 ) is employed to enhance the photovoltaic performance of methylammonium lead iodide (MAPbI 3 )-based PSCs by improving the film quality and optimizing the photoelectronic properties of halide perovskites. It is found that Ac − and Sb 3+ of Sb(Ac) 3 play different roles and their synergistic effect contributed to the eventual excellent photovoltaic performance of MAPbI 3 -based PSCs with a power conversion efficiency of above 21%. The Ac − anions act as a crystal growth controller and are more involved in the improvement of perovskite film morphology. By comparison, Sb 3+ cations are more involved in the optimization of the electronic structure of perovskites to tailor the energy levels of the perovskite film. Furthermore, with the assistance of Sb(Ac) 3 , MAPbI 3 -based PSCs deliver much improved moisture, air, and thermal stability. This work can provide scientific insights on the additive engineering for improving the efficiency and long-term stability of MAPbI 3 -based PSCs, facilitating the further development of perovskite-based optoelectronics.
Xuan Liu,Xinxin Xia,Qiuquan Cai,Feilong Cai,Liyan Yang,Yu Yan,Tao Wang
We report efficient, planar heterojunction perovskite solar cells prepared via bar coating that are compatible with large-scale fabrication on flexible substrates . Our MAPbI 3 perovskite devices by bar coating method achieved a maximum power conversion efficiency (PCE) of 13.0% using a ITO/PEDOT: PSS/CH 3 NH 3 PbI 3 (MAPbI 3) /PCBM/Ag structure, and there is very weak hysteresis in these devices. After formulation of the precursor solution and optimization of the coating process , planar perovskite thin films containing large-size grains with low surface roughness were obtained. We found that anti-solvent plays an important role in determining the uniformity, size of grains and width of grain boundaries in perovskite films. The addition of 5 vol% isopropanol into the precursor solution leads to the formation of large aspect ratio grains with a length ca. 200 µm and width of a few hundred nanometers , together with narrow grain boundaries. However, the absence or excessive of isopropanol result in perovskite films with high surface roughness and broad grain boundaries due to inefficient crystal growth or the formation of ridges between crystal grains. These grain boundaries have high PL intensity due to charge recombination and consequently deteriorate device efficiency. When bar-coating the perovskite films in air, best devices with PCE over 11% can be achieved with a relatively high humidity around 50%, eliminating the low humidity requirement during air processing.
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