Pyrophosphate interlayer improves performance of semi-transparent perovskite solar cells

Hybrid perovskite solar cells (PSCs) with high average visible transmission (AVT) are applicable to building-integrated photovoltaics (BIPV) and windows. Reducing perovskite thin film thickness is an ideal approach that does not require complex processing methods to achieve high AVT. However, it has been challenging to fabricate high quality perovskite film thin enough to achieve the AVT requirement for BIPV applications without compromising overall optoelectronic properties. In this work, we improve the crystallization of perovskite film and enhance interface properties by incorporating a potassium pyrophosphate (KPP) interlayer between the bottom electron transporting layer and the perovskite photoactive layer. This results in superior optoelectronic characteristics in PSCs, with power conversion efficiency (PCE) of up to 16%, at which the AVT can reach up to 36% (measured without opaque metal contacts), while also demonstrating improved long-term stability. To investigate material potential as semi-transparent PSC, 5 cm x 5 cm semi-transparent mini-modules were fabricated; they exhibited PCEs of up to 9.8% at a high AVT of 30%. These modules exhibited high stability under both simulated light and in an outdoor environment, tracked for over 1000 h and 75 days, respectively. Hybrid perovskite solar cells (PSCs) with high average visible transmission (AVT) are applicable to building-integrated photovoltaics (BIPV) and windows.