Cation Influence on Hot-Carrier Relaxation in Tin Triiodide Perovskite Thin Films

Slow hot-carrier cooling may potentially allow overcoming the maximum achievable power conversion efficiency of single-junction solar cells. For formamidinium tin triiodide, an exceptional slow cooling time of a few nanoseconds was reported. However, a systematic study of the cation influence, as is present for lead compounds, is lacking. Here, we report the first comparative study on formamidinium, methylammonium, and cesium tin triiodide thin films. By investigating their photoluminescence, we observe a considerable shift of the emission peak to high energy with the increase of the excited-state population, which is more prominent in the case of the two hybrid organic-inorganic perovskites (∼45 meV vs ∼15 meV at 9 × 10¹⁷ cm^-3 carrier density). The hot-carrier photoluminescence of the three tin compositions decays with a 0.6-2.8 ns time constant with slower cooling observed for the two hybrids, further indicating their importance.