Dipropyl sulfide optimized buried interface to improve the performance of inverted perovskite solar cells

Recently, [4–(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) has garnered significant attention as a highly effective passivation layer for NiOx. However, the Me-4PACz passivation layer shows low wettability to perovskite precursors, hindering the crystallization of perovskite. Moreover, Me-4PACz does not uniformly and completely cover NiOx, failing to achieve an optimal passivation effect. The presence of high-valence-state Ni species and reactive hydroxyls on the NiOx film surface leads to perovskite degradation. To address this, dipropyl sulfide (DPS) was incorporated into a solution of Me-4PACz. This approach not only enhances the wettability of Me-4PACz, facilitating the growth of larger perovskite grains but also enables Me-4PACz to form a homogeneous passivation layer with strong coverage. This effectively prevents direct contact between NiOx and perovskite films. Additionally, DPS interacts with reactive hydroxyls, removing them from the NiOx surface and mitigating the deprotonation reaction of MA/FA in perovskite. Furthermore, DPS is reducible, which helps in reducing high-valent Ni (Ni4+), thereby decreasing redox reactions at the interface. As a result, the optimized perovskite solar cells with DPS achieved a power conversion efficiency (PCE) of 22.29%, higher than the control device of 20.52%. Moreover, the DPS-decorated device demonstrated excellent stability, retaining over 80% of its initial PCE value, compared to only 60% retention in the control device. This work modified the buried interface and offers valuable insights for subsequent similar studies.