Hole-Transporting Vanadium-Containing Oxide (V2O5–x) Interlayers Enhance Stability of α-FAPbI3-Based Perovskite Solar Cells (∼23%)

Perovskite solar cells (PSCs) have attracted tremendous interest due to their outstanding intrinsic photovoltaic properties, such as absorption coefficients, exciton binding energies, and long carrier lifetimes. Although the power conversion efficiency (PCE) of PSCs is close to the Si solar cells' PCE, device stability remains a challenge. In particular, the device stability is more critical in n-i-p normal structured PSCs, which show a higher efficiency than p-i-n inverted ones, simply because of the much lower stability of 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spi). To prevent the devices from degrading performances arising both from perovskite's degradation and Spi instability, we prepare atomic layer deposition (ALD)-grown transition metal oxides for hole transport with efficient n-i-p PSCs. We demonstrate low-temperature (T_dep = 45 °C)-grown amorphous ALD-V₂O_5-x with oxygen-deficient traps on top of Spi as an interlayer, which prevents the devices' degradation in performance. By blocking moisture and oxygen, ALD-V₂O_5-x was able to greatly improve the devices' stability by preserving the photovoltaic α-FAPbI₃ phase while suppressing both Li ion diffusion from the additive and Au ions from the electrode. As a result, we successfully fabricate PSCs with passivation/hole-transporting bifunctional Spi/ALD-V₂O_5-x interlayers without sacrificing photovoltaic performances, and the device stability is significantly improved.