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