Variable Temperature Hot Casting Study of 2D Perovskite Thin Films

Three-dimensional perovskites (3DP) have soared to the forefront of modern thin-film solar cell technology owing to their remarkable optoelectronic properties. These properties allow the creation of devices with power conversion efficiencies exceeding 27% steadily approaching the Shockley-Quesser limit. Despite these positive characteristics, 3DP are often inadequate and degrade when subjected to environmental conditions such as changes in temperature, moisture levels, or even sunlight itself. Ruddlesden-Popper phase two-dimensional perovskite (2DP) films are a direct counterpart to 3D perovskites and have shown great stability when compared to 3DP. However, 2DP-based devices tend to suffer from problems attributed to inherent poor charge transport characteristics caused by organic cations which act like spacers between the conductive inorganic layers. To improve charge transport we can improve the morphology of the 2DP, ideally making the film near single-crystalline quality. Near single crystal perovskites have a strongly preferential out-of-plane alignment with respect to contacts in planar devices facilitating improved charge transport. In this article, we report on how changes in temperature, specifically during fabrication, can affect the crystallography of 2DP. To examine film morphology after production, both optical and SEM images were taken of each fabricated device showing uniform films as well as unique amorphous structures. Photoluminescent spectroscopy (PL) was performed for each annealing temperature illustrating a red shift with increasing temperatures. I/V measurements were also taken to monitor the charge transport characteristics of each respective film with current levels in the nA range. An increase in current is noted from 100 to 145 degrees Celsius before dropping down at higher temperatures. Lastly, solar cells were fabricated with 2DP absorber layers hot casted at various temperatures with the peak PCE at around 2%.