Efficient fully textured perovskite silicon tandems with thermally evaporated hole transporting materials

Abstract

Fully textured perovskite silicon tandem solar cells effectively minimize reflection losses and are compatible with industrial silicon production lines. To facilitate the scalability and industrial deployment of perovskite silicon tandems, all functional layers, including the perovskite layer, must be deposited with scalable techniques. Currently, self-assembling molecules (SAMs), polymeric and low-molecular-weight organic semiconductors, are widely used as hole transport layers (HTLs) in p-i-n structured perovskite solar cells. Usually, SAMs are deposited using the spin coating method, but the use of this method could be challenging with large area textured silicon substrates, leading to inhomogeneous SAM layers and lossy HTL/perovskite interfaces. To address this issue, we investigated thermal evaporation of SAMs (2PACz and Me-4PACz) and some other HTLs, such as TaTm and Spiro-TTB. We examined the effect of varying HTL thicknesses on device performance and showed that the thickness of the thermally evaporated HTLs significantly affects the open circuit voltage (VOC) and fill factor (FF) of solar cells. Furthermore, using ultraviolet photoemission spectroscopy and Suns-VOC measurements, we correlated the changes observed in the VOC and FF with HTL thickness variations to changes in energy band positions (loss in hole selectivity) and effective resistance losses, respectively. With the optimized HTL thickness, we obtained ∼30% efficiency in 1 cm2 area and ∼26% in 4 cm2 area tandem devices.