Utilizing a Soft IZO Sputtering Process to Contact Buffer-Free Semitransparent Perovskite Pin Solar Cells

Perovskite solar cells in pin structure are considered as advantageous for the implementation in perovskite silicon tandem solar cells. So far, one drawback of this approach is the requirement of buffer layers (e.g. SnOx) between the front TCO and the carbon-based ETLs (e.g. C60 or PCBM). In this work, we show that a sufficiently soft process for indium zinc oxide sputtering allows a damage-free contacting of the pin-structure directly on top of the ETL (C60) while simultaneously enabling a leaner processing scheme by abandoning the need for a (ALD) buffer layer. Ray tracing simulations indicate a gain of 0.44 mA/cm² in photo generation in perovskite top cells by omitting the SnOx buffer layer. For the optimized IZO sputter process, we obtain implied open circuit voltages in absolute photoluminescence measurements at least as high as for reference samples without IZO. The sputter process works for both vapor and wet chemically deposited perovskite solar cells. Under the constrains of an oxygen-free sputter process, our soft process leads to a 60 nm thick IZO layer with a high mobility of µ= 42.7 ± 0.3 cm²/V s and low charge carrier density $N= 3.6 \pm 0.02 \times 10^{20} 1/\text{cm}^{3}$.