2D BA2PbI4 Regulating PbI2 Crystallization to Induce Perovskite Growth for Efficient Solar Cells.

Using seeds to control the crystallization of perovskite film is an effective strategy for achieving high-efficiency perovskite solar cells (PSCs). Owing to their excellent environmental stability brought by their long alkyl chain, n-butylammonium (BA) cations are widely used for fabricating efficient and stable PSCs. However, BA-based 2D perovskite is seldom been investigated as a seed. Here, BA2PbI4 is employed to regulate the crystallization of PbI2, acting as nucleation centers. As a result, porous PbI2 film with high crystallinity is obtained, which allows the realization of perovskite film with preferential crystal orientations of (001) and large grain size of over 2 µm. The corresponding PSC achieves a high power conversion efficiency (PCE) of 24.30% and exhibits satisfactory stability, retaining 91.70% of the initial PCE after 300 h of thermal aging at 85°C.

Cyclic Multi-Site Chelation for Efficient and Stable Inverted Perovskite Solar Cells.

Trap-assisted non-radiative recombination losses and moisture-induced degradation significantly impede the development of highly efficient and stable inverted (p-i-n) perovskite solar cells (PSCs), which require high-quality perovskite bulk. In this research, we mitigate these challenges by integrating thermally stable perovskite layers with Lewis base covalent organic frameworks (COFs). The ordered pore structure and surface binding groups of COFs facilitate cyclic, multi-site chelation with undercoordinated lead ions, enhancing the perovskite quality across both its bulk and grain boundaries. This process not only reduces defects but also promotes improved energy alignment through n-type doping at the surface. The inclusion of COF dopants in p-i-n devices achieves power conversion efficiencies (PCEs) of 25.64% (certified 24.94%) for a 0.0748-cm2 device and 23.49% for a 1-cm2 device. Remarkably, these devices retain 81% of their initial PCE after 978 hours of accelerated aging at 85˚C, demonstrating remarkable durability. Additionally, COF-doped devices demonstrate excellent stability under illumination and in moist conditions, even without encapsulation.