Guanidine carbonate modified TiO2/Perovskite interface for efficient and stable planar perovskite solar cells

The rational design and modification of the buried interface are essential and challenging for high-performance perovskite solar cells (PSCs). TiO₂ is a simple and readily available electron transport layer material, but its surface defects and poor interfacial contact with perovskite layers hinder its widespread application. Here, we propose an effective TiO₂/perovskite interface modification strategy by introducing simple guanidine carbonate (GuaCO₃) onto the surface of TiO₂. Guanidine carbonate can improve the interfacial contact between TiO₂ and perovskite, reduce non-radiative recombination, and enhance carrier extraction. Moreover, the PbI₂ film grown on the TiO₂/GuaCO₃ substrate tended to become porous during the preparation of perovskite films by the traditional two-step method, which facilitated the complete reaction of organic ammonium salts with PbI₂ and promoted the growth of high-quality perovskite films. The experimental results indicate that GuaCO₃ can passivate the interfacial defects of TiO₂/perovskite, as well as reduce the accumulation of interfacial charges. The device modified with GuaCO₃ achieved a power conversion efficiency (PCE) of 23.39 %, which is significantly higher than that of the control device (21.73 %). After storage in an ambient environment at room temperature for 600 h, the unencapsulated device modified with GuaCO₃ retained 78 % of its initial efficiency, while the control device retained only 57 % of its initial efficiency. These results indicate that interfacial modification with GuaCO₃ is an effective strategy for improving the performance of PSCs.