Development and non-toxic and stable perovskites for high efficiency solar cells
The efficiency of halide perovskite solar cells has dramatically increased from 9% to 22% in less than 5 years.1 They have shown promise toward the future for low cost and highly efficient solar electricity. While there are still considerable rooms for device optimization, it is now the time to tackle the device long-term stability and toxicity challenges. The presence of Pb in the champion material, methylammonium lead iodide CH3NH3PbI3, may prevent this technology from large-scale deployment due to environmental and health concerns. Attempts have been made in replacing Pb with other non-toxic metals such as Sn, Bi, or Sb.2-6 Long-term device stability is another challenge that needs to be addressed. To meet the commercialization standard, solar cells are required to produce stable performance for at least 10000 hours. This is at present still a goal to reach because halide perovskite thin films are relatively unstable to moisture, heat, and light. Preventing the interaction of halide perovskite with moisture is thus a crucial task. Successful examples of improving the moisture-stability of halide perovskite solar cells are layered two-dimensional perovskites,7-9 metal oxide overlayers,10 and carbon-based encapsulation.11 The goal of this project is two-fold: to address the moisture instability of halide perovskites by introducing a new class of moisture-resistant light absorbing materials, namely two-dimensional (2D) Ruddlesden–Popper hybrid lead iodide perovskites, where hydrophobic butylammonium CH3(CH2)3NH3+ long chains are intercalated into the three-dimensional (3D) CH3NH3PbI3 framework, and ultimately to develop stable, environmental-friendly, and efficient halide perovskite solar cells by employing 2D lead-free Sn-based perovskites.