2, Wright Center for Photovoltaics Innovation and Commercialization, Toledo, Ohio, United States
Monolithic integrated thin film tandem solar cells consisting of a high bandgap perovskite top cell and a low bandgap thin film bottom cell are expected to reach higher power conversion efficiencies (PCEs) with lower manufacturing cost and environmental impacts than the market-dominated crystalline silicon photovoltaics. There have been several demonstrations of 4-terminal and 2-terminal perovskite tandem devices with CuInGaSe2 (CIGS) or CuInSe2(CIS). However, these devices employed the CH3NH3PbI3 top cells with a bandgap of 1.55 eV, which is not optimal for the tandem configuration. Further advance will be enabled by tuning the bandgap and thickness of the perovskite absorber to maximize the photocurrent limited by the current match condition. Here, we systematically study the optical absorption and transmission of perovskite thin films with varying absorber layer thickness and band gap and demonstrate high efficiency bifacial transparent perovskite devices. Based on these results, we model the photocurrent generations in both perovskite and CIS subcells and estimate the performances of projected tandem devices by integrating the fabricated perovskites on an ideally functioning CIS device. Our results show that optimal bandgap for the perovskite layer is 1.7 to 1.8 eV, and the optimal thickness is 300 to 500 nm, depending on the bandgap of the perovskite film. With these configurations, PCEs above 20% could be achieved by monolithically integrated perovskite/CIS tandem solar cells.