Incorporating self-assembled silane-crosslinked carbon dots into perovskite solar cells to improve efficiency and stability

Carbon dots (CDs) have significant potential in the chemical decoration, crystal modification, and surface passivation of perovskite photovoltaics. However, incompatibility between the hydrophilic/hygroscopic nature of CDs and moisture sensitive perovskite remains an issue. Solving this problem would yield a significant improvement for stable perovskite devices embedded with CDs. Herein, hydrophobic passivation layers are realized for perovskite solar cells (PSCs) through the surface engineering of CDs, exploiting electrostatic self-assembly of trichloro(3,3,3-trifluoropropyl)silane (C3H4Cl3F3Si) and CDs. The embedded CDs modify perovskite grains and passivate grain boundary defects, thereby promoting the carrier lifetime and charge collection. The inserted C3H4Cl3F3Si insulating layer provides a tunneling junction at the contact of the perovskite and electron transport layer. This tunneling layer can selectively conduct electrons and block holes, which spatially separate photo-generated carriers to suppress their recombination. As a result, the optimized perovskite devices deliver the highest efficiency of 21.12% with a high fill factor of 82.86%. Moreover, the variation of surface wettability can be achieved by the self-assembly of C3H4Cl3F3Si, which improves the stability of perovskite devices by maintaining nearly 90% efficiency for over 30 days' exposure to an ambient atmosphere without encapsulation.