混合阳离子钙钛矿相分离机理及抑制策略研究

Long-term stability is the most dramatic challenge that hinders the commercialization of perovskite solar cells (PSCs). Hybrid perovskite materials with multiple A-site components with improved stability are considered as promising candidates for stable PSCs. However, due to the large radius differences between different cations, mixed A-site perovskites could suffer from spontaneous phase segregation, that a single inter-mixing phase separates into two or more phases. Phase segregation deteriorates the power conversion efficiency and limits the long-term stability of mixed cation PSCs. Few studies have investigated the phase segregation processes in mixed cation perovskites, which leads to a lack of understanding of their origins and influencing factors. We proposed to (1) quantitatively analyze the phase compositions of mixed perovskites using X-ray diffraction (XRD) and Raman characterizations, (2) investigate the course of phase segregation using in-situ measurements, (3) study the microstructure and phase distribution of separated phases using microscopic tools. We proposed to investigate the intrinsic and external factors that influence the phase segregation process, including chemical compositions, grain size, crystallinity, temperature, humidity, and illumination. Based on these results, we aim for understanding the thermodynamic driving forces and kinetic mechanism of the phase segregation process in mixed A-site perovskites and developing suppression strategies, which would be beneficial for improving the long-term stability of PSCs and perovskite optoelectronic devices.

长期稳定性是阻碍钙钛矿太阳能电池大规模应用的瓶颈问题。在钙钛矿A位中加入多元阳离子，可以改善其稳定性。但由于离子尺寸差异，混合钙钛矿的混合相会发生相分离，分解为多相混合物，导致太阳能电池性能下降。混合阳离子钙钛矿的相分离制约了钙钛矿太阳能电池长期稳定性的提高，但目前对于相分离行为的研究仍十分欠缺，对其影响因素和发生机理的认识不够深入。因此，本项目拟利用XRD、Raman等物相表征手段，定量分析混合钙钛矿的物相组成；利用原位表征，研究混合钙钛矿相分离的结构演化过程；利用微观结构表征技术，探索混合钙钛矿相分离后的物相分布规律。通过研究不同成分、晶粒尺寸、结晶度的混合钙钛矿在高温、高湿度、光照等条件下的相分离行为，揭示影响相分离过程的材料本征特性及外界环境因素，以期阐明导致相分离的热力学和动力学机理，并提出抑制混合钙钛矿相分离的策略，为构建高效稳定的钙钛矿太阳能电池和光电器件奠定理论和技术基础。

有机无机杂化钙钛矿材料具有优异的光电性能，是近年兴起的一种新型光伏材料。其中混合阳离子钙钛矿因其性能优异，稳定性高，受到了广泛的关注。然而混合钙钛矿中A位阳离子迁移的活化势垒小，容易发生离子迁移，进而引起相分离和太阳电池稳定性下降。针对混合阳离子钙钛矿的相分离引起电池长期稳定性下降的问题，本项目以FA-Cs二元钙钛矿为主要研究对象，探索了混合A位阳离子钙钛矿相分离的表征手段，利用荧光光谱、吸收光谱和X射线衍射多种手段表征了混合钙钛矿的相分离过程，发现相分离生成了富FA相和δ-CsPbI3相。研究发现相分离的多种影响因素，发现在同时具有光照和加热的条件下相分离程度最大，在钙钛矿中加入Br元素和二维钝化可以降低相分离倾向，在商用SnO2胶体中存在的K+可以诱导相分离的产生。通过共聚焦荧光显微镜发现相分离优先发生在晶界处，二次相在晶界处形核长大。通过二维钝化、改进电子传输层和钙钛矿成分优化，可以抑制混合钙钛矿的相分离，将混合钙钛矿电池的效率提升到24.47%，持续光照下稳定工作500小时效率保持初始值的90%。