Optimization of MoOΧ Buffer Layer for Single-Junction and Four-Terminal Perovskite-Silicon Tandem Solar Cells

Abstract

Semi-transparent solar cells based on wide-bandgap perovskites have gained great attention due to their potential application of smart windows and tandem devices. MoO_Χ is one of the most commonly used buffer materials in high performance semi-transparent solar cells, whereas the deposition technique of this key layer has been rarely discussed. Herein, a systematical comparison of MoO_Χ deposited by sputtering and thermal evaporation and their impact to solar cells performance have been studied. Through various characterizations, we found that the hole transporting layer is more vulnerable during the sputtering process even with mild condition, causing an escape of the 4-tert-butylpyridine additive and damage of the electrical contact of the interface. Voltage dependent photoluminescence study indicates that the hole transfer process within the device has been hindered, leading to a notable decline in performance and the exhibition of S-shaped J-V curves. In contrast, the impact of thermally evaporated MoO_Χ is negligible, making it more suitable for the preparation of high-performance devices. By using thermally evaporated MoO_Χ, semi-transparent solar cells based on 1.70 eV perovskite have achieved a champion efficiency of 20.5% and it retained 96% of the initial efficiency after 30 days. When combined with silicon cells, an efficiency of 28.9% for four-terminal perovskite-silicon tandem solar cells have been achieved.