Bifunctional modified biopolymer for highly efficient and stable perovskite solar cells and modules

Perovskite solar cells are promising and competitive candidates for future photovoltaic technologies. However, the fabrication of high-quality, efficient, large-area perovskite solar cell modules (PSCMs) is still one of the most significant challenges for future commercialization. In this study, we introduce a sulfonic acid group into poly-l-lysine (PLL) via a one-step ring-opening reaction, and the modified PLL with a sulfonic acid group (PLLS) is expected to synergistically modify the interface between the TiO2 and perovskite layers. The sulfonic acid group in PLLS can modify the electron transport layer by inactivating the under-coordinated titanium (Ti) ion, which reduces the oxygen vacancies and defects on the surface of the TiO2 film and increases the conductivity. In addition, amine groups can passivate deep-level defects on the surface of perovskite to reduce non-radiative recombination. The power conversion efficiency (PCE) of a unit device (0.14 cm2) is increased from 20.60 % to 22.98 % after PLLS modification. The unencapsulated device retained ∼ 80 % of its initial efficiency after 960 h in ambient air with humidity of approximately 10 %. Moreover, the PSCMs achieved a PCE of 20.07 % (with a notable fill factor of 76.75 %) over an active area of 33 cm2 and showed excellent operating stability.