Rapid thermal annealing process for Se thin-film solar cells†

Recently, selenium (Se) has regained interest as a possible wide-bandgap photovoltaic material for silicon-based tandem applications. However, the easy sublimation of Se below the melting point (220 °C) brings challenges for high-quality Se thin films. Herein, we design a rapid thermal annealing (RTA) method to balance the contradiction between the sublimation and crystallization of Se thin films. Through optimizing the annealing temperature, a high-quality Se thin film is obtained with a large grain size (～1 μm) and preferred [003] orientation during the RTA process. Then, an optimized efficiency of 3.22% is achieved in a ZnO/Se heterojunction solar cell. This study provides a new guide to obtain high-quality Se thin film by RTA and the method can be extended to other materials with high saturated vapor pressure.