Perovskite photovoltaic cells with ultra-thin buffer layers for tandem applications

Perovskite photovoltaic cells (PVs) and their tandem application with silicon PVs are strong candidates for low-cost energy harvesting device. To utilize efficient perovskite-based tandem devices, parasitic absorption from buffer layers should be minimized. Here, we demonstrated an infrared (IR)-transparent perovskite PV employing ultra-thin buffer layers. Since vacuum-deposited layers follow underlying structure, thermally evaporated thin buffer layer (<15 nm) successfully covers perovskite film. These thin buffer layers provide selective carrier transport to the electrode because of their high energy barrier (>1 eV) compared to active layer. Moreover, as a result of reduced parasitic absorption, the transmittance of device with thin buffer layers is over 80% at near IR region (800-1100 nm), which allows low energy photons to penetrate top cell of tandem device. The engineering of a top perovskite PV and stacking it with commercialized silicon PVs lead to 19.4% (four-terminal) efficient tandem devices.