Semitransparent Solar Cells with Ultrasmooth and Low-Scattering Perovskite Thin Films

Semitransparent solar cells can be applied to photovoltaic windows, which harvest light from both sides. Here we report that the visual transparency of perovskite solar cells can be improved by suppressing the optical scattering at the perovskite layer, through making the surface ultrasmooth, without undue reduction of the perovskite thickness and efficiency. Ultrasmooth perovskite films prepared by a short spinning with vacuum drying method, mean roughness of which is 6 nm or lower, exhibit suppressed scattering (<2%) and high visual transparency. The power conversion efficiency (PCE) of 14.26% is achieved with a thick Ag top electrode (100 nm). A semitransparent cell with a thin Ag top electrode (10 nm) coated with MoO 3 (20 nm) exhibits scattering of <1% and PCE of 11.0 and 8.7% for the front and back incidence, respectively. The ultrasmooth and compact preovskite layer leads also to fast photocurrent responses with negligible or sufficiently small hysteresis.