有机金属卤化物钙钛矿太阳能电池中离子移动现象的研究

Organometal trihalide perovskite (OTP) solar cells have attracted broad attention in recently years as a new renewable energy technology. Its power conversion efficiency quickly increased from 3.8% to over 20% after only six years of investigations, making this technical very promising. However, OTPs is still facing some problems. It was discovered by the principal investigator (PI) that there are significant mobile ions in the OTP films, bringing problems in accurate characterization of the device efficiency and impairing the stability of the OTP solar cells. Accordingly, addressing the ion migration problem becomes a very important topic in the field of OTPs. Here the PI plans to carry out systematic studies on the ion migration effect in OTPs by means of composition variation and post-treatment. A series of OTPs materials/devices with varied composition will be fabricated, and the impacts of ionic radius, ionic electronegativity and lattice tolerance factors on the generation and migration of mobile ions will be investigated. Post treatment, such as atmosphere annealing, will be carried out to adjust the defects concentration in OTP films and the corresponding impacts on ion migration will be analyzed. The proposed researches will lead to systematic understandings about the generation and migration of mobile ions in OTPs, and developing knowledges for the design of mobile-ions-free OTPs materials.

近几年基于有机金属卤化物的钙钛矿太阳能电池引起研究人员的广泛关注，其能量转换效率仅六年便从3.8%上升至20%以上，被视为是一种极具实用前景的可再生能源技术。但是，钙钛矿太阳能电池仍有诸多基础科学问题有待解决。申请人的前期研究证实钙钛矿薄膜中具有大量可移动离子，它们不仅会引起光电流迟滞而干扰器件性能评估，而且将严重影响器件效率和稳定性，阻碍钙钛矿太阳能电池的实用化。因此，研究钙钛矿薄膜中的离子移动成为钙钛矿太阳能电池领域的重要研究课题。在申请人前期研究基础上，本申请项目拟通过钙钛矿材料的组分构成、可控气氛处理、薄膜后处理工艺等研究，揭示离子尺寸、电负性、以及离子尺寸失配程度等对可移动离子的产生和移动的影响规律，阐明空位缺陷浓度和杂质分子对钙钛矿薄膜中离子移动的影响机制，从而为消除钙钛矿材料中的离子移动、开发新型没有移动离子的钙钛矿材料体系以及提高钙钛矿材料长期稳定性提供理论和实验基础。

从改善材料本征稳定性入手，研究提升钙钛矿太阳电池的工作寿命在当前具有非常重要的意义。在本项目研究中，为了更好地理解钙钛矿太阳电池在光照、电场、氧气吸附等复杂条件下的老化机理，我们揭示了离子迁移与钙钛矿薄膜光氧老化过程存在相互加剧的协同作用。通过开展A位离子调控策略，成功利用Cs+离子掺杂抑制了钙钛矿中离子迁移和超氧离子产生率，显著降低了MA基和FA基钙钛矿在光氧条件下的老化速率。为了开发具有低离子迁移趋势、高光伏效率的钙钛矿活性层，我们聚焦准二维（2D）钙钛矿材料体系并研究了材料的形核、结晶、成膜过程。首先提出并论证了类三维钙钛矿表面作为模板诱导准2D钙钛矿定向生长的机理模型，揭示了溶液中准2D钙钛矿晶体形成择优面外取向的成因。通过采用少量Rb+离子作为结晶抑制剂调节PEA基准2D钙钛矿的结晶速率，提升了薄膜结晶质量和相应电池效率。我们研究证实DJ型准2D钙钛矿有利于抑制钙钛矿薄膜中的离子迁移，并发现准2D钙钛矿的层间距低至4.56 Å时仍然可以有效抑制离子迁移。为了研制无电流迟滞、低能量损失的钙钛矿太阳电池，我们利用硅酞箐分子、可交联二元胺分子对钙钛矿表面进行缺陷钝化，先后研制出无富勒烯传输层或非辐射开压损失低至0.1 V的倒置钙钛矿电池器件。在基金委的资助下，相关系列研究成果发表于国内外同行普遍认可的高质量国际及国产期刊，完成了项目设定的考核指标。