籽晶诱导的两步法制备含Cs的高效稳定钙钛矿太阳能电池

The power conversion efficiency of organic-inorganic hybrid perovskite solar cells has reached more than 22% due to its excellent optoelectronic properties. However, the stability issue remains as big challenge for its real applications. Introduction of inorganic cations such as Cs or Rb can improve the stability of mixed organic cation-based perovskite solar cells. Nevertheless, this kind of solar cells suffer from low efficiency due to large band gap. (FAPbI3)1-x(MAPbBr3)x(x<0.05) perovskite solar cells have ideal band gap and the best efficiency, but still poor stability. To solve the problem, we put forward a new method-perovskite seeding method to prepare high-quality Cs contained mixed cation perovskite film. This method includes a two-step method where Cs-contained perovskite seeds were first introduced into PbI2 thin film and then the organic ammonium salt was spin-coated onto the PbI2 film. The introduced perovskite seeds can provide the Cs source and act as nuclei to facilitate perovskite crystallization during the reaction of alkylammonium halide with PbI2. Perovskite seeding method can effective solve the difficulty of incorporating the (stabilizing) Cs cation in sequentially-deposited film. The nucleation and grain size can be precisely tuned and the growth speed can be fastened, Cs cations can be effectively introduced into the film. The proposed idea can provide important insights of perovskite film control and is expected to further improve the intrinsic stability of mixed cation perovskite solar cells, which is a real step forward toward real applications of perovskite photovoltaics.

有机无机钙钛矿材料由于优异的光电性质，电池光电转化效率已突破22%，但是稳定性一直饱受诟病。无机离子的加入可大幅提升电池稳定性，但纯无机材料的电池效率较低。成份为 (FAPbI3)1-x(MAPbBr3)x(x<0.05)的钙钛矿材料拥有理想的禁带宽度，创造了钙钛矿电池的效率记录，但是稳定性不佳。针对以上问题，本项目创新性的提出一种全新的籽晶诱导生长法来制备高质量Cs掺杂的混合阳离子钙钛矿薄膜。通过在PbI2薄膜中引入含Cs钙钛矿籽晶的两步法生长，使PbI2薄膜中的籽晶提供后续钙钛矿生长的成核位点，引导高质量薄膜生长，并且提供Cs源，解决两步法中无机阳离子有效掺杂的问题。通过籽晶诱导，可实现对成核和晶粒大小的精确调控，加快薄膜生长速度，有效掺入无机Cs离子，对深入研究钙钛矿材料的成膜控制具有重要的学术价值，并有望大幅提高钙钛矿太阳能电池的本征稳定性，为钙钛矿电池的实际应用迈出坚实的一步。

碳中和的时代背景对清洁能源提出了更高的要求，太阳能作为一种可免费获取，全球分布广，持续存在，绿色无污染的清洁能源，具有巨大的应用前景和商业价值。钙钛矿材料是相比传统光伏材料具有更多优点的新兴光伏材料，但其能量转换效率目前还低于传统太阳能电池，进一步探索其晶体生长机理并提升器件的效率与稳定性仍是钙钛矿光伏走向商业应用前所要解决的难题。该项目从底层材料晶体质量出发，提出了全新并普适的钙钛矿籽晶诱导法，利用籽晶提供后续钙钛矿生长的成核位点，实现了对钙钛矿晶粒尺寸和成膜动力学的调控，大幅提升了电池的光电转化效率与运行稳定性。进一步，提出并发展出在前驱液中引入CsCl和含Br籽晶的方法，进一步实现对钙钛矿成分的精确调控，将太阳能电池器件的最优效率提高到 22.1%，持续工作500小时后保持85%的初始效率。继而在开拓的籽晶诱导法领域进行深耕，发现了高取向二维钙钛矿籽晶对钙钛矿薄膜晶面取向的高度调控作用，实现了具有高强度且高纯度的(001)超高质量钙钛矿薄膜，将电池的光电转化效率大幅提升至24.0%，稳定性提升至1000小时。关于籽晶诱导的系列研究工作为从晶体生长的底层设计制备高质量的钙钛矿材料提供了重要的研究思路，为进一步提升钙钛矿太阳能电池的光电转化效率和稳定性奠定了优异的材料基础。本项目发表SCI学术期刊论文11篇，申请发明专利3项。多篇工作发表在能源材料领域知名国际期刊如Joule，Advanced Materials，Advanced Energy Materials，Advanced Functional Materials等上。其中有关二维籽晶调控三维钙钛矿晶面取向的相关工作结果发表在全球新锐能源类顶级期刊Joule 6, 1 (2022), 并受Cell Press对话科学家栏目邀约，以“二维调三维！北大赵清团队大幅提升钙钛矿太阳能电池效率”为题进行了重点报道和访谈。该项目的实施为我国在新能源钙钛矿太阳能电池领域的发展起到了积极的推动作用，为我国早日实现碳中和贡献了力量。