1 Introduction Hybrid and all-inorganic lead halide perovskites have been widely studied in optoelectronics,[1-4] photovoltaics,[5-8] and thermoelectric applications[9] due to their high light-to-electricity,[10, 11] ultra-low thermal conductivity,[12-14] high charge mobility,[15, 16] and high Seebeck coefficients.[17] They possess a general formula of ABX3, where A denotes an organic cation such as methylammonium (MA+) or formamidinium (FA+), or Cs+ ion, B is divalent Pb2+ or Sn2+, and X is...