Du Tian, Macdonald Thomas J, Yang Ruo Xi, Li Meng, Jiang Zhongyao, Mohan Lokeshwari, Xu Weidong, Su Zhenhuang, Gao Xingyu, Whiteley Richard, Lin Chieh-Ting, Min Ganghong, Haque Saif A, Durrant James R, Persson Kristin A, McLachlan Martyn A, Briscoe Joe
School of Engineering and Materials Science and Materials Research Institute, Queen Mary University of London, London, E1 4NS, UK.
Department of Materials and Centre for Processable Electronics, Imperial College, London, W12 0BZ, UK.
Adv Mater. 2022 Mar;34(9):e2107850. doi: 10.1002/adma.202107850. Epub 2022 Jan 23.
Formamidinium lead triiodide (FAPbI ) is attractive for photovoltaic devices due to its optimal bandgap at around 1.45 eV and improved thermal stability compared with methylammonium-based perovskites. Crystallization of phase-pure α-FAPbI conventionally requires high-temperature thermal annealing at 150 °C whilst the obtained α-FAPbI is metastable at room temperature. Here, aerosol-assisted crystallization (AAC) is reported, which converts yellow δ-FAPbI into black α-FAPbI at only 100 °C using precursor solutions containing only lead iodide and formamidinium iodide with no chemical additives. The obtained α-FAPbI exhibits remarkably enhanced stability compared to the 150 °C annealed counterparts, in combination with improvements in film crystallinity and photoluminescence yield. Using X-ray diffraction, X-ray scattering, and density functional theory simulation, it is identified that relaxation of residual tensile strains, achieved through the lower annealing temperature and post-crystallization crystal growth during AAC, is the key factor that facilitates the formation of phase-stable α-FAPbI . This overcomes the strain-induced lattice expansion that is known to cause the metastability of α-FAPbI . Accordingly, pure FAPbI p-i-n solar cells are reported, facilitated by the low-temperature (≤100 °C) AAC processing, which demonstrates increases of both power conversion efficiency and operational stability compared to devices fabricated using 150 °C annealed films.
碘化甲脒铅（FAPbI₃）因其约1.45 eV的最佳带隙以及与甲基铵基钙钛矿相比提高的热稳定性，对光电器件具有吸引力。传统上，纯相α-FAPbI₃的结晶需要在150°C进行高温热退火，而所得的α-FAPbI₃在室温下是亚稳态的。在此，报道了气溶胶辅助结晶（AAC）方法，该方法仅使用含碘化铅和碘化甲脒的前驱体溶液，不添加化学添加剂，在仅100°C的温度下就能将黄色的δ-FAPbI₃转化为黑色的α-FAPbI₃。与在150°C退火的样品相比，所得的α-FAPbI₃表现出显著增强的稳定性，同时薄膜结晶度和光致发光产率也有所提高。通过X射线衍射、X射线散射和密度泛函理论模拟确定，通过较低的退火温度和AAC过程中的结晶后晶体生长实现的残余拉伸应变的松弛，是促进相稳定的α-FAPbI₃形成的关键因素。这克服了已知会导致α-FAPbI₃亚稳态的应变诱导晶格膨胀。因此，报道了纯FAPbI₃ p-i-n太阳能电池，其通过低温（≤100°C）AAC工艺制备，与使用150°C退火薄膜制造的器件相比，功率转换效率和运行稳定性均有所提高。
