Uniform Cs 2 SnI 6 Thin Films for Lead-Free and Stable Perovskite Optoelectronics via Hybrid Deposition Approaches

Abstract

Abstract: Herein, we synthesized uniform Cs 2 SnI 6 films by two kinds of hybrid deposition methods by considering volume expansion involved during phase transformations. First, oblique thermal evaporation for CsI followed by SnI 4 spin-coating resulted in uniform Cs 2 SnI 6 films free of impurity phases. The rapid expansion (within 10 s of spin-coating) from CsI to Cs 2 SnI 6 (Δ V= 106 %) was accommodated by porous CsI films inhibiting crack formation. Excess SnI 4 on the Cs 2 SnI 6 after spin-coating was effectively removed by toluene washing without any damages to Cs 2 SnI 6 , and optimum deposition parameters were suggested in terms of carrier mobility. Second, annealing CsI with SnI 4 vapor at 250 °C and post-annealing in the SnI 4 and I 2 vapor at 300 °C produced Cs 2 SnI 6 film with complete coverage. The slow reaction (70 min for a complete conversion) provided sufficient time for complete diffusion of SnI 4 into CsI without crack formation even with compact CsI. The nonradiative recombination path in Cs 2 SnI 6 was suppressed by post-annealing in the SnI 4 - and I 2 -atmosphere, as confirmed from the enhanced photoluminescence.