Modifying buried heterogeneous contacts to promote efficient carrier extraction for efficient perovskite solar cells

Tin dioxide (SnO₂) as electron transport layer (ETL) prepared by chemical bath deposition (CBD) method in perovskite solar cells (PSCs) has achieved excellent certified efficiency. However, the fabrication of CBD SnO₂ inevitably induces the defect generation at surface, which results in hysteresis and instability of the device under light illumination. To overcome this challenge, it is crucial to modify the buried interface. 4-chlorothiophenol (4CTP) is employed on top of SnO₂, which effectively passivates the surface chemisorbed non-lattice oxygen as well as oxygen vacancies, reduces the interfacial defect states, and suppresses the phase instability and undesired PbI₂ species. Moreover, enhanced perovskite film quality and improved energy level alignment at heterogeneous interfaces promote efficient electron carrier extraction. Therefore, the modified device exhibits substantial improvements in V_OC, J_SC and FF, particularly V_OC increases from 1.15 to a respectable 1.20 V, with the optimized champion power conversion efficiency (PCE) of 25.80 %. The 4CTP-treated PSC retains 85 % of the initial PCE after 800 h at 40 °C, whereas the control device shows a 22 % decay in PCE. The 4CTP-treated device maintains 83 % of its initial power after 180 h of maximum power point tracking tests in N₂ atmosphere. This highlights the potential of 4CTP treatment as a promising strategy for advancing PSC technology.