Solution-processed metal halide perovskite semiconductors, such as CH₃NH₃PbI₃, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I₂ back into I^-, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.

Nature Communications 6, Article number: 10030 doi:10.1038/ncomms10030
Received 11 May 2015 Accepted 28 October 2015 Published 30 November 2015

http://www.nature.com/ncomms/2015/151130/ncomms10030/full/ncomms10030.html

可溶液加工的金属卤化钙钛矿半导体（如 CH₃NH₃PbI₃）展现了很高的能量转化效率，尽管它也存在着不可忽视的缺陷态密度问题。一种可能的原因是钙钛矿晶体中存在卤素空缺或是存在金属铅，这导致 I/Pb 的化学计量比不平衡。 Zhang 等人发现，无论从电学角度还是从形貌角度讲，在前驱体溶液中加入一定量的次磷酸（HPA）可以显著的提高钙钛矿薄膜的质量和荧光强度。这使得电池具有更高的能量转化效率和重复性。研究发现，HPA可以将氧化的I₂还原成 I^-，最终提升了钙钛矿晶体中的化学计量比。（新材料在线）