Minimizing sputter damage-induced electrical losses in monolithic perovskite/silicon tandem solar cells during deposition of the transparent front-electrode

The front electrode of monolithically integrated perovskite/silicon tandem solar cells commonly consists of a transparent conductive oxide (TCO). TCOs are usually deposited using the well-established method of magnetron sputtering. High particle energies, however, can cause sputter damage to sensitive substrates during the deposition process. Therefore, a SnO2 buffer layer is used in all current perovskite top-cell designs with p-i-n polarity and competitive efficiencies. Here, we propose a methodology to identify electrical losses in perovskite solar cells (PSC) caused by sputter damage during the TCO deposition. We also show a simple method for minimizing sputter damage to the PSC, which enables SnO2 buffer layer-free devices. Evaluation of the ideality factor and pseudo-current density-voltage (J-V) curves, reconstructed from light intensity-dependent J-V measurements on tandem top-cell-equivalent semi-transparent single-junction PSCs, revealed that sputter damage causes transport and non-radiative recombination losses. These losses result in a lower open-circuit voltage (VOC) and fill factor (FF), limiting the PSC performance. By lowering the sputter power density, we reduced the impact of sputter damage. This resulted in improved VOCs (similar to 13 mV) and FFs (similar to 3%) of the semi-transparent PSCs, which is a direct consequence of the reduced electrical losses[1]. Finally, we applied our low-damage sputter approach on SnO2 buffer layer-free monolithic perovskite/silicon tandem devices. Compared to tandem devices with a SnO2 buffer layer, the SnO2 buffer layer-free devices were optically superior, resulting in a device current density improvement of 0.52 mA/cm(2) due to increased current densities in both sub-cells[1]. This is an important development for further optical performance optimization of tandem devices. [1] M. Hartel et al., 'Reducing sputter damage-induced recombination losses during deposition of the transparent front-electrode for monolithic perovskite/silicon tandem solar cells', vol. 252, no. October 2022, pp. 1-7, 2023, doi: 10.1016/j.solmat.2023.112180.