Tailoring buried interface of tin oxide-based n-i-p perovskite solar cells via bidirectional and multifunctional metal ion chelating agent modification

For the n-i-p perovskite solar cells hiring tin oxide (SnO2) as electron transporting material, the buried interface (SnO2/perovskite interface) acts as the working interface and growth substrate of the perovskite crystal simultaneously. Nevertheless, problems such as severe non-radiative recombination, energy level mismatch, poor interface contact, and chemical reactions exist on this interface, leading to undesirable efficiency loss and instability. In regard to this, we employ the metal ion chelating agent ethylenediaminetetraacetic acid tetrasodium salt (EDTA4Na), which consists of six chelating sites (afforded by four COO- and two nitrogen atoms) and alkaline metal ion (Na+), as a bidirectional and multifunctional buried interface modifier. It has been established that EDTA4Na can effectively passivate defects and strengthen interface contact via the robust chelating interaction between SnO2 and the perovskite layer, demonstrating better energy level alignment and enhanced electron mobility for charge transport. Moreover, the sodium ions can diffuse into the perovskite film to manipulate its crystallization process and decrease the defect density. Accordingly, the device modified by EDTA4Na delivers a champion power conversion efficiency of 22.77% (15.9% higher than the control device-19.64%), and V-oc is significantly increased from 1.066 V to 1.140 V. The optimized device retains 96% of its initial performance after aging for 1000 h, exhibiting evident enhancement when compared to the one based on pristine SnO2. Thus, a practical and effective tactic to mitigate the efficiency loss and instability of perovskite solar cells is presented.