Tellurium-Based Double Perovskites A₂TeX₆ with Tunable Band Gap and Long Carrier Diffusion Length for Optoelectronic Applications

Lead-free hybrid perovskites have attracted immense interest as environmentally friendly light absorbers. Here, we report on tellurium (Te)-based double perovskites A 2 TeX 6 (A = MA, FA, or BA; X = Br – or I –; MA = CH 3 NH 3; FA = CH(NH 2 ) 2; BA = benzylamine) as potentially active materials for optoelectronic devices. These perovskites exhibit a tunable band gap (1.42–2.02 eV), a low trap density (∼10 10 cm –3 ), and a high mobility (∼65 cm 2 V –1 s –1 ). Encouragingly, the MA 2 TeBr 6 single crystal with a band gap of 2.00 eV possesses a long carrier lifetime of ∼6 μs and corresponding carrier diffusion lengths of ∼38 μm, which are ideal characteristics for a material for photodetectors and tandem solar cells. Moreover, A 2 TeX 6 perovskites are relatively robust in ambient conditions, being stable for at least two months without showing any signs of phase change. Our findings bring to the forefront a family of lead-free Te-based perovskites for nontoxic perovskite optoelectronics.