Standing 1D Chains Enable Efficient Wide-Bandgap Selenium Solar Cells

The recent surge in tandem solar cells and indoor photovoltaics has renewed interest in selenium (Se), the world's first photovoltaic material, due to its intrinsic wide bandgap of ≈1.9 eV, high stability, and non-toxicity in small quantities when applied in photovoltaics. However, with a 1D chained crystal structure, Se tends to grow crystalline films with a lying orientation-chains parallel to substrates arising from the low surface energy; this results in poor carrier transport across chains held together by weak van der Waals forces. Here a substrate-heating strategy that facilitates the interfacial bonding between Se and substrate is introduced, enabling the growth of Se films with a standing orientation-chains perpendicular to substrates. This achieves efficient carrier transport along covalently bonded chains. The resulting Se films thereby exhibit a fourfold increase in carrier mobility compared to lying-oriented Se films. Consequently, Se solar cells are achieved with the highest power conversion efficiency of 8.1% under AM1.5G 1-sun illumination. The unencapsulated devices exhibit negligible efficiency loss after 1 000 h of storage under ambient conditions.