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Abstract In hybrid perovskite solar cells (PSCs), the reaction of hydrogens (H) located in the amino group of the organic A-site cations with their neighboring halides plays a central role in degradation. Inspired by the retarded biological activities of cells in heavy water, we replaced the light H atom with its abundant, twice-as-heavy, nonradioactive isotope, deuterium (D) to hamper the motion of H. This D substitution retarded the formation kinetics of the detrimental H halides in Pb-based PSCs, as well as the H bond-mediated oxidation of Sn2+ in Sn–Pb-based narrow-bandgap PSCs, evidenced by accelerated stability studies. A computational study indicated that the zero point energy of D-based formamidinium (FA) is lower than that of pristine FA. In addition, the smaller increase in entropy in D-based FA than in pristine FA accounts for the increased formation free energy of the Sn2+ vacancies, which leads to the retarded oxidation kinetics of Sn2+. In this study, we show that substituting active H with D in organic cations is an effective way to enhance the stability of PSCs without sacrificing photovoltaic (PV) performance. This approach is also adaptable to other stabilizing methods. 

The AzRISE-TEP Solar Test Yard is a 600-module capacity test bed that provides the environment for in-situ testing of PV module performance, with real-time data collection of module power production and local weather conditions. This work involves the examination of flexible, semi-transparent, organic photovoltaic (OPV) modules in an outdoor testing environment to study degradation in the hot, arid, Tucson, AZ climate. The work reports on changes in the I-V performance and efficiency of a string of two OPV modules in order to estimate degradation experienced by the OPV modules. The study finds that the module string under test dropped to below 80% of its initial power conversion efficiency (PCE) after 54.58 days, and predicts that the PCE will drop below 50% of its initial state after 114.53 days from deployment. Keywords: Organic Photovoltaics, OPV, degradation, field testing, reliability, outdoor