Molecular Engineering of Self-Assembled Monolayers for Inverted Wide-Bandgap Perovskite Solar Cells and Perovskite-Silicon Tandem Solar Cells

Minimizing interfacial defect states is crucial in perovskite photovoltaics, especially considering the layered structure of perovskite solar cells. Self-assembled monolayers (SAMs) exhibit impressive optoelectrical properties by passivating defect states at the substrate or the perovskite bottom surface. However, non-uniform SAM formation results in unpredictable interfacial properties between the SAM and the perovskite layer. Here, we improve the quality of the buried interface between the SAM and perovskite through molecular engineering of the SAM solution. The introduction of the Lewis base molecule, 1-acetylguanidine (AG), in the SAM film facilitates the formation of highly ordered SAM molecules on the substrate via mixed interactions of ionic and hydrogen bonding. In addition, the SAM film with AG shows a strong interaction with undercoordinated lead ions at the perovskite bottom surface, effectively suppressing interfacial recombination losses and improving energy-level alignment due to change in work function. With the ordered SAM molecules and minimized buried interface defects, we achieve impressive power conversion efficiencies of 22.54% and 21.19% for active areas of 0.096 cm² and 1.00 cm², respectively, with an open-circuit voltage (V_oc) of 1.27 V in wide-bandgap perovskite solar cells. Furthermore, when combining the molecularly engineered SAM with silicon bottom solar cells, we achieve a PCE of 29.90% (1.00 cm²), while retaining over 80% of the initial PCE after over 500 hours of operation.