Fully Vacuum Deposited Perovskite Solar Cells in Substrate Configuration

Vacuum-deposition of perovskite solar cells (PSCs) in substrate configuration on metal thin films and foils is advantageous. Due to the high conductivity of the bottom-metal electrode, the possibility of depositing thick and narrow metal grids on the top transparent electrode for facilitating loss-free charge extraction, and the intrinsic scalability of the vacuum-deposition methods, large-area cells, or subcells for modules can be fabricated with relative ease. However, despite the above, the number of reports focusing on the fabrication of PSCs in substrate configuration remains scarce. In this work, we demonstrate the complete fabrication of inverted PSCs in substrate configuration by vacuum-deposition methods. The resultant devices (~0.05 cm²) having a co-evaporated formamidinium methylammonium lead iodide (FAMAPI, E_g of ~1.54 eV) perovskite demonstrate a maximum power conversion efficiency (PCE) of ~19%, which is comparable to the maximum PCE of ~19.5 % obtained in the superstrate configuration devices and is the highest value reported for a PSC in substrate configuration. The devices in substrate configuration exhibit higher short circuit current density values despite the parasitic absorbance from the front fullerene-C₆₀ layer (> 0.5 mA/cm²). Furthermore, we discuss the reflection losses in the above two device configurations based on the insights obtained from the transfer matrix-based optical simulations. Next, we observe that the encapsulated devices of both the configurations exhibit similar thermal stability at 85 °C (on a hotplate) in an N₂ environment, reaching a t₈₀ (time to reach 80% of the original PCE) of ~800 hours. Finally, via systematic characterization, we study and identify the degradation mechanisms occurring in the devices and propose recommendations for enhancing their thermal stability. We believe our findings may contribute to the development of large-area, efficient, and thermally stable fully vacuum-deposited PSCs.