Ultrahigh Electrical Conductivity in p-Type CsPbI₂Br Perovskite Thin Films by Modulation Doping

The widespread adoption of halide perovskites for application in thermoelectric devices, DC power generators, and lasers is hindered by their low charge carrier concentration. In particular, increasing their charge carrier concentration is considered the main challenge to serve as a promising room-temperature thermoelectric material. Efforts have been devoted to enhancing the charge carrier concentration by doping and composition engineering. However, the coupling between charge carrier concentration and mobility, along with the poor stability of these materials, impedes their development for thermoelectric applications. Herein, we demonstrate the successful increase in the charge carrier concentration of CsPbI₂Br by forming a heterojunction structure with Cu₂S via a facile spin-coating method. The excellent band alignment between two materials combined with a charge-transfer mechanism realizes the modulation doping, resulting in 8 orders of magnitude increase in carrier concentration from 10¹² to 10²⁰ cm^-3 without detrimental effect on the carrier mobility of CsPbI₂Br. The thermoelectric power factor of the heterostructured CsPbI₂Br reached 6.6 μW/m·K², which is 330 times higher than that of pristine CsPbI₂Br. Furthermore, these films showed higher humidity stability than the control films. This study offers a promising avenue for increasing the charge carrier concentration of halide perovskites, thereby enhancing their potential for various applications.