Two-Dimensional Layered Perovskite Solar Cells with 12.5 % Efficiency and 2000 Hours Stability in Light and Humidity

Three-dimensional organic-inorganic perovskites have emerged as one of the most promising thin-film solar cell materials due to their remarkable photophysical properties that have led to power conversion efficiencies exceeding 22%, with the prospect of further improvements towards Shockley-Queisser limit for a single‐junction solar cell (~33.5%). Alongside efficiency, a critical factor for photovoltaics and other optoelectronic applications is environmental and photostability under operating conditions. In contrast to their 3D counterparts, Ruddlesden-Popper phases, layered two-dimensional (2D) perovskite films, have shown promising stability, but poor efficiency at only 4.73%. This is attributed to the inhibition of out-of-plane charge transport by organic cations, which act like insulating spacing layers between the conducting inorganic components. Here we overcome this fundamental issue in layered perovskites by producing near single-crystalline quality thin-films with a strongly preferential out-of-plane alignment of the inorganic perovskite component to facilitate efficient charge transport. We report a photovoltaic efficiency of 12.5 % with no hysteresis, and devices that exhibit greatly improved stability in comparison to their 3D counterparts when subjected to aggressive stress tests of light, humidity and heat. Unencapsulated 2D perovskite devices retain over 70% of their efficiency for over 2000 hours under constant 1 Sun illumination, and exhibit greater tolerance to 65% relative humidity than 3D equivalents. When the devices are encapsulated, the layered devices do not show any degradation under constant 1 Sun illumination or humidity.