Molecule-bridged electron-selective contact for high-efficiency halide-based perovskite solar cells

Tin oxide (SnO₂) is a frequently used electron transport material in n-i-p type perovskite solar cells (PSCs). However, a large number of defects are present at the ETL/perovskite interface (also known as the buried interface), which will significantly limit the formation of high-quality perovskite films, thereby reducing the device performance of PSCs. Herein, malic acid (H₂Mi) was introduced as a bidirectional cross-linking agent at the buried interface for the first time to construct a molecular bridging layer to improve the electron extraction of SnO₂ and the growth of perovskite crystals. The multifunctional cross-linking layer can not only passivate the trap states of Sn interstitials (Sn_i) and oxygen vacancies (V_O) and thereby improve the conductivity of SnO₂, but also regulate the growth of perovskite crystals and inhibit non-radiative recombination due to its strong interaction with undercoordinated Pb²⁺ as a Lewis base. As a result, the H₂Mi-modified PSCs achieved an impressive 24.34% champion power conversion efficiency (PCE). In addition, perovskite films and PSCs based on H₂Mi modification show excellent long-term stability. After being placed in ambient air for 1080 h, the unencapsulated target device can maintain more than 90% of the initial PCE. After 400 h of maximum power point (MPP) tracking test under continuous illumination (100 mW cm⁻²), the unencapsulated target device can maintain 80% of the initial PCE. The excellent performance of the device shows that this strategy can be used as an effective passivation method for buried interface defects in PSCs to further promote their commercialization.