The intriguing properties of halide perovskites have led to high-performance optoelectronic devices. Recently, tin (Sn) halide perovskites have attracted significant interest for thermoelectrics owing to their high electrical conductivity and low thermal conductivity. In this work, we evaluate the thermoelectric performance of Sn and binary tin-lead (Sn-Pb) hybrid perovskites. Leveraging the oxidative nature of Sn, air treatment of the perovskite films led to improved thermoelectric performance due to self-doping. The film conductivity increases significantly with a semiconductor to quasi-metallic transition upon air exposure. In addition, this enhanced electrical conductivity was preserved after controlled air exposure for extended period of time. An increase of 42% and 83% in the thermoelectric power factor of CH3NH3SnI3 and CH3NH3Sn0.75Pb0.25I3 was observed, respectively after air treatment compared to pristine films at 336 K. Apart from thermoelectrics, the implications of this work are relevant to other perovskite devices such as solar cells and LEDs.