Ultrahigh Electrical\nConductivity in p‑Type\nCsPbI<sub>2</sub>Br Perovskite Thin Films by Modulation Doping

The widespread adoption of halide perovskites for application\nin\nthermoelectric devices, DC power generators, and lasers is hindered\nby their low charge carrier concentration. In particular, increasing\ntheir charge carrier concentration is considered the main challenge\nto serve as a promising room-temperature thermoelectric material.\nEfforts have been devoted to enhancing the charge carrier concentration\nby doping and composition engineering. However, the coupling between\ncharge carrier concentration and mobility, along with the poor stability\nof these materials, impedes their development for thermoelectric applications.\nHerein, we demonstrate the successful increase in the charge carrier\nconcentration of CsPbI<sub>2</sub>Br by forming a heterojunction structure\nwith Cu<sub>2</sub>S via a facile spin-coating method. The excellent\nband alignment between two materials combined with a charge-transfer\nmechanism realizes the modulation doping, resulting in 8 orders of\nmagnitude increase in carrier concentration from 10<sup>12</sup> to\n10<sup>20</sup> cm<sup>–3</sup> without detrimental effect\non the carrier mobility of CsPbI<sub>2</sub>Br. The thermoelectric\npower factor of the heterostructured CsPbI<sub>2</sub>Br reached 6.6\nμW/m·K<sup>2</sup>, which is 330 times higher than that\nof pristine CsPbI<sub>2</sub>Br. Furthermore, these films showed higher\nhumidity stability than the control films. This study offers a promising\navenue for increasing the charge carrier concentration of halide perovskites,\nthereby enhancing their potential for various applications.