Ultrathin chromium oxide buffer layer by reactive thermal deposition for high-performance semitransparent perovskite solar cells

Transparent conductive oxide (TCO) films are widely used for semitransparent perovskite solar cells (st-PSCs) and perovskite-based tandem solar cells due to their high optical transparency and good electrical conductivity. However, the high-power sputtering damage during the deposition of TCO film is a vital factor to prevent the perovskite-based solar cells from achieving high efficiency. In this work, we develop an ultrathin chromium oxide (CrOx) buffer layer between the hole transporting layer (HTL) and indium-doped tin oxide (ITO) by trace-oxygen reactive thermal deposition (to-RTD). The experimental results show that the CrOx buffer layer can hinder the sputtering damage of ITO deposition and ensure a high-performance device, which can be attributed to the improved conductivity of the HTL/CrOx/ITO structure together with the tailored energy level alignment. In addition, this buffer layer with a thickness of 4 nm displays a high optical transmittance (>95%) in the interested wavelengths, meaning a limited optical parasitic absorption loss. As a result, the st-PSC with CrOx buffer layer achieves champion power conversion efficiency (PCE) of 19.06%, which is one of the highest PCEs for the n-i-p st-PSCs. Moreover, a four-terminal perovskite/silicon tandem solar cell featuring a CrOx buffer layer realizes a relatively high PCE of 27.48%.