Directional\nRegulation of Photogenerated Carriers\nin Tin Halide Perovskites for Enhanced Thermoelectrics

Metal\nhalide perovskites hold good prospects for thermoelectric\napplications. Photoexcitation is manifested to effectively increase\n carrier density of perovskites, yet the severe carrier recombination\ndue to the bipolar effect leads to the significant Seebeck voltage\nloss. Herein, we discover a remarkably photo-enhanced thermoelectric\neffect in FASnI<sub>3</sub> thin film by depositing an electron transport\nlayer, delivering a 28-fold enhancement in thermoelectric power factor\n(PF). It is found that carrier recombination is greatly suppressed\nvia directional regulation of photogenerated carrier transport, leading\nto a concurrent increase of electrical conductivity (σ) and\nSeebeck coefficient (<i>S</i>). Such a strategy is applicable\nto other compositional tin perovskite films with higher carrier and\ndefect densities, which are however less pronounced owing to the inferior\nphotocarriers and the restrained electron extraction. Nonetheless,\nwe achieve a champion PF up to ∼342 μW m<sup>–1</sup> K<sup>–2</sup> in CsSnI<sub>3</sub> films by virtue of their\noutstanding σ that plays a decisive role in comparison to that\nof <i>S</i>.