Atomic and Molecular Hydrogen Impurities in Hybrid Perovskite Solar Cells

Hydrogen interstitials are expected to be important in organic-inorganic hybrid perovskites; however, the characteristics and behaviors of hydrogen in perovskites remain poorly understood. Here, on the basis of density functional theory calculations, we quantitatively reported that both atomic and molecular hydrogen interstitials can form in hybrid MAPbI(3) and MASnI(3) perovskites. Whereas molecular hydrogen interstitial, H-2, is chemically inert, atomic hydrogen interstitial, Hi, serves as an electrically active negative-U defect. We identify high-density Hi(+) as a significant origin of ionic conductivity in p-type MAPbI(3) under the hydrogen-rich conditions, with the calculated activation energy being comparable to that measured in experiments. The highly diffusive Hi(+) ions are expected to impact hysteresis, charge separation, device polarization, and photogenerated field-screening effect and consequently degrade the solar cell performance. We evaluated approaches for mitigating such detrimental effects and suggested that synthesizing the perovskites with slightly extra iodine addition or tin alloying can effectively suppress the concentration of Hi(+). Our results are important to understand the fundamental aspects of hydrogen in perovskites in general and offer valuable insight for further improving the performance of perovskite solar cells and other optoelectronic devices via defect engineering.

Automated summary

This study reveals the formation of atomic and molecular hydrogen interstitials in organic-inorganic hybrid perovskites and their impact on the performance of perovskite solar cells. It shows that atomic hydrogen interstitials serve as electrically active defects and can enhance ionic conductivity, leading to degradation in the solar cell performance. However, the detrimental effects of hydrogen can be mitigated by controlling the concentration through alloying or iodine addition.