Unveiling heavy heterovalent doping-modulated microstructure and thermoelectric performance in bulk hybrid perovskite single crystals

Abstract

Organic-inorganic hybrid metal halide perovskites have emerged as a promising candidate for low-temperature thermoelectric conversion. However, challenges remain in heavily doping bulk perovskite single crystals without phase segregation or self-doping compensation issues to increase the carrier concentration. Previous efforts to enhance their thermoelectric performance rely on photoexcitation or surface/interface doping, which is not suitable for bulk devices to work in dark. This study achieves high monovalent and trivalent doping concentrations of up to 5 % in bulk single crystals of MAPbI3 and MAPbBr3 without phase segregation or defect formation. For monovalent doping, K+ and Li+ are incorporated into the perovskite lattice as interstitials. The resulting lattice distortion/microstrain enhances the electrical conductivity by 10 ∼ 100 times of undoped samples at 420 K. Trivalent doping using SbCl3, BiBr3, and BiI3 significantly enhances the carrier concentration and electrical conductivity, up to 1012 cm−3 and 0.038 S m−1 for MAPbBr3 with 10 % BiI3 at 465 K, respectively, which is 105 times of the undoped samples and 10 times of the best reports on doped MAPbBr3. Interestingly, the Bi3+ dopant oxidizes the deep defect state Pb0, resulting in Bi+ and Pb2+ formation and contributing to the enhanced electrical conductivity. Enhanced thermoelectric figure of merit (ZT) is achieved in MAPbBr3 with 5 % BiI3 at 315 K, almost 100 times of the best reports on doped MAPbBr3. This study provides fundamental understanding of doping-modulated microstructural, charge carrier, and thermoelectric properties of hybrid halide perovskites, offering potential doping strategies to realize the theoretically predicted promising thermoelectric properties in their bulk single crystals for practical thermoelectric devices. The doping-modulated carrier transport will also guide the optimization of optoelectronic applications of halide perovskites for solar cells, light emitters, and photodetectors.