Doping-free Janus homojunction solar cell with efficiency exceeding 23%

Abstract

Photovoltaic solar cell is one of the main renewable energy sources, and its power conversion efficiency (PCE) is improved by employing doping or heterojunction to reduce the photogenerated carrier recombination. Here, we propose a straightforward strategy for constructing high-PCE homojunction solar cells, where intrinsic driving forces can simultaneously enhance the efficiency of carrier separation and transport. Thanks to the intrinsic dipole of Janus structure, doping-free Janus homojunction has naturally not only a type-II band alignment to promote the photoexciton dissociation, but also a reduced effective bandgap to enhance light absorption. More importantly, the interfacial dipole can facilitate the separation of carriers into different layers, thereby promoting carrier separation; and the intrinsic dipole across the Janus structure can drive photoinduced electron and hole transfer to opposite layers, enhancing carrier transport. We illustrate the concept in titanium-based Janus monolayer homojunction, where the theoretically observed PCE reaches 23.22% of TiSSe homojunction. In contrast to the previous cell architectures that require complex processing procedures and often result in defects, the doping-free homojunction configuration promises both high PCE and significantly lower manufacturing costs. Our work opens an avenue to design low-cost, high-efficiency solar cells.