Highly conductive n-type CH3NH3PbI3 single crystals doped with bismuth donors

Abstract

Highly conductive n-type bismuth-doped CH₃NH₃PbI₃ (MAPbI₃:Bi) single crystals are successfully grown by the inverse temperature crystallization (ITC) method using bismuth iodide as the dopant source. As revealed by XRD analysis, the Bi-doped MAPbI₃ single crystals maintain a perfect cubic perovskite structure (Pmm). Bi³⁺ ions are successfully incorporated into the MAPbI₃ crystal lattice, which induces three orders of magnitude enhancement in the n-type electrical conductivity in a controllable way. Clear Urbach tails in the optical absorption spectra and continuous blue shifts in the room-temperature photoluminescence (PL) spectra are both observed after bismuth doping, which indicates the formation of bismuth induced donors and the release of more electrons to the conduction band. Temperature-dependent PL (TDPL) studies are adopted to study the optical fingerprints of bismuth induced donor defects in the MAPbI₃ crystals. By analyzing the TDPL spectra in detail, it is found that the bound exciton (D⁰X) peak in doped MAPbI₃:Bi has a stronger relative intensity and also a significant redshift in comparison with the pristine MAPbI₃ crystal. This indicates that stable donor levels are formed in MAPbI₃:Bi single crystals by bismuth doping. These results suggest that n-type perovskite crystals have been realized in a controlled doping way, and potential applications in bipolar perovskite-based optoelectronic devices could be realized.