Efficient Fully Textured Perovskite Silicon Tandems with Thermally Evaporated Hole Transporting Materials

Abstract

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