Orthogonally Arranged Bimolecular Passivation: Sequential Interface Engineering Improves Charge Transfer at the Perovskite/PCBM Interface

Although surface passivation has significantly contributed to the rapid increase in the power conversion efficiency (PCE) of p-i-n perovskite solar cells (PSCs), the nonradiative recombination and energy level alignment at the perovskite/PCBM interface are still the key factors affecting the overall efficiency of p-i-n PSCs. Herein, a sequential interface engineering (SIE) strategy is developed to enhance charge transfer at the perovskite/PCBM interface in inverted p-i-n perovskite solar cells. <i>p</i>-Anisidine-2-sulfonic acid (pAsA) is used to passivate surface defects on the perovskite layer. Its multiactive-site binding aligns with the Pb²⁺ ion spacing on the perovskite surface. Then, vertically aligned ethylenediamine diiodide (EDAI₂) is introduced into the perovskite/PCBM interface, forming dipoles to further passivate defects, reduce nonradiative recombination, and improve energy level alignment. The rationality of orthogonal bimolecular passivation is proven by theoretical calculations. The SIE strategy not only suppresses nonradiative recombination but also optimizes the surface morphology and energy level alignment at the interface. As a result, the MA-free inverted perovskite solar cells achieve a remarkable power conversion efficiency of 24.85%, and the stability is significantly enhanced by retaining 84.92% of the initial efficiency after 2000 h of MPP tracking under room-temperature conditions. The work underscores the potential of a synergistic passivation approach for advancing the performance and stability of PSCs.