Photo-energy conversion efficiency of CH3NH3PbI3/C60 heterojunction perovskite solar cells from first-principles

Abstract

Halide perovskites have emerged as the most potential candidate for the next-generation solar cells. In this work, we conduct a comprehensive first-principles study on the photo-energy conversion efficiency (PCE) of the CH₃NH₃PbI₃/C₆₀ heterojunction. Since perovskite solar cells (PSCs) are generally exposed to substantial temperature variations that affect the photo-physics and charge separation in the perovskites, finite slabs of both the tetragonal- and cubic-phases of CH₃NH₃PbI₃ (MAPbI₃) are constructed with different orientations of the methylammonium (MA) cation with respect to the perovskite surface. A C₆₀ molecule, acting as an electron acceptor and transport material, is introduced at various positions on the MAPbI₃ surface. Using the detailed balance approach, the PCE of the heterojunction is determined by examining the Kohn–Sham energies and orbitals located either in MAPbI₃ or in C₆₀. Our study reveals that the stability, the exciton dissociation efficiency, and the PCE of the tetragonal MAPbI₃/C₆₀ heterojunctions strongly depend on the MA orientation and the C₆₀ position on the MAPbI₃ surface. This is attributed to the polar behavior of MAPbI₃. Using the tetragonal-phase heterojunction, a high PCE of η ∼ 19% can be achieved, if certain surface conditions are met. Built-in electric field originating from the surface dipoles of the MA cation facilitates the dissociation of electron–hole pairs and the electron transfer to fullerene. On the other hand, the heterojunction with a high-temperature cubic MAPbI₃ structure exhibits a PCE of η ∼ 10%, regardless of the MA orientation and C₆₀ on the MAPbI₃ surface.