Directional Regulation of Photogenerated Carriers in Tin Halide Perovskites for Enhanced Thermoelectrics

Abstract

Metal halide perovskites hold good prospects for thermoelectric applications. Photoexcitation is manifested to effectively increase carrier density of perovskites, yet the severe carrier recombination due to the bipolar effect leads to the significant Seebeck voltage loss. Herein, we discover a remarkably photo-enhanced thermoelectric effect in FASnI₃ thin film by depositing an electron transport layer, delivering a 28-fold enhancement in thermoelectric power factor (PF). It is found that carrier recombination is greatly suppressed via directional regulation of photogenerated carrier transport, leading to a concurrent increase of electrical conductivity (σ) and Seebeck coefficient (S). Such a strategy is applicable to other compositional tin perovskite films with higher carrier and defect densities, which are however less pronounced owing to the inferior photocarriers and the restrained electron extraction. Nonetheless, we achieve a champion PF up to ∼342 μW m^–1 K^–2 in CsSnI₃ films by virtue of their outstanding σ that plays a decisive role in comparison to that of S.