Halide perovskites have recently attracted a lot of attention owing to their potential for realizing high-efficient low-cost photovoltaics. Among the halide perovskites, methyl-ammonium lead tri-iodide CH₃NH₃PbI₃ (MAPbI₃) is one of the most widely studied compounds. Fullerenes have been widely used as the electron acceptor layers for planar-heterojunction perovskite solar cells due to their superior abilities in electron capture and transport. We perform a first-principles study on the electronic structures and photo-energy conversion efficiency of fullerene on MAPbI₃. Finite slabs of both the tetragonal- and cubic-phases of MAPbI₃ with different orientations of the methylammonium (MA) cation are constructed with respect to the perovskite surface. A fullerene C₆₀ is introduced at various positions on the MAPbI₃ surface. Photo-energy conversion (PCE) efficiency of the heterojunction perovskite solar cell is examined from the detailed balance limit by examining the Kohn–Sham energies and orbitals located either in fullerene or MAPbI₃. We found that the stability, the exciton dissociation efficiency, and the PCE of a tetragonal MAPbI₃/C₆₀ heterojunction strongly depend on both the MA orientation and the absorption position of C₆₀ on the MAPbI₃ surface. However, the heterojunction with a cubic MAPbI₃ structure does not show an obvious dependence on the orientation of MA and the absorption position of C₆₀.

Khian-Hooi Chew is currently an associate professor at the Department of Physics, University of Malaya. Prior to joining University of Malaya. He was a research associate and university postdoctoral fellow at the department of Applied Physics, the Hong Kong Polytechnic. In year 2006 to 2009, he joined the School of Physics, the University of Western Australia as a postdoctoral fellow. He was the TWAS-UNESCO Associate for the Institute of Atomic & Molecular Science of Academia Sinica, Taiwan. He is a member of the International Advisory Committee (IAC) of the Molecular Science and Technology (MIST) Program under the Taiwan International Graduate Program (TIGP) of Academia Sinica, Taiwan. He is currently serving as a member of both the Executive Board of the Asian Ferroelectric Association (AFA) and the Asian Electroceramics Association (AECA). He received the ACCMS Mid-Career Award (2017) from the Asian Consortium Computational Materials Science (ACCMS). His current research interests include first-principles and phenomenological studies of ferroelectrics and multiferroics, perovskites, 2D materials, energy and quantum materials.