以富碘配体为晶核的无铅类钙钛矿材料及光伏性能研究

The transition metals are easily accessible by chelation of Halogens to form chelate metal complexes. Lead-halogen complexes allow fabrication of multilayer devices via solution processes by increasing solubility in the polar solvent, which is a type of additive with great potential. In spite of intensive research in this area, the device performance is still far from what might be expected, and the reason for this discrepancy remains poorly understood. Recently, we used the lead sulfide with iodide-rich ligand into the lead based perovskite precursor solution. Due to the multidentate iodide ligand simultaneously chelates bivalent lead and thus reduces the activation energy of the growth of perovskite crystals. The crystallinity can be promoted. Furthermore, iodide chelated bivalent lead helps in nucleation sites focus, thus the crystal growth space is expanded. The average grain size is increased from the 500nm, when the iodide-rich ligand was not added, to 4μm. Based these findings, this program develops new optimization method and principle of environmentally friendly lead-free perovskite photovoltaic devices, achieving the formulation of large crystalline grain perovskite with high crystallinity and the promotion of conversion efficiency. Centering on the goals and aiming at materials of iodide-rich ligand, heterogeneous nuclei of lead-free perovskite crystal growth is found able to improve the crystallinity of crystal and corresponding morphology. Throughout this project, the internal essence of the effect of iodide-rich ligand on devices is mastered from the aspects of crystal growth, property of thin film, device performance and so on, thus clarifying the working mechanism of iodide-rich ligand, providing theoretical guidance for the crystal growth of lead-free perovskite and offering new ideas for the optimization of device performance.

卤素易与过渡金属鳌合形成簇合物，铅类卤素簇合物易溶于极性溶剂，进而改善多层器件的溶液制程，是一类非常有潜力的添加剂。目前的研究主要致力于小分子卤化物的开发，但过少的卤素源使鳌合作用局限。最近，我们将具有富碘配体的硫化铅加入铅钙钛矿前驱物溶液，因为多齿碘配体同时鳌合二价铅而降低钙钛矿成长的活化能，所以提升结晶性；更进一步，碘源鳌合大量二价铅帮助成核点集中，晶体成长空间因此扩大，平均晶粒由未添加富碘配体时的500nm提升至4μm。本项目在此基础上，发展环保型无铅钙钛矿光伏器件优化的新方法和原理，实现高结晶性的大晶粒钙钛矿且同时提升转换效率。围绕目标针对富碘配体材料，作为无铅类钙钛矿晶体成长的异质晶核，提升晶体的结晶性与形貌。通过项目实施，将从晶体成长、薄膜性质和器件性能多方面掌握富碘配体对器件影响的内在本质，澄清工作机制。为无铅类钙钛矿的晶体生长提供理论指导，进而为器件性能的优化提供新的思路。

本项目旨在发展钙钛矿光伏器件优化的新方法和原理，通过富碘配体为晶核以实现高结晶性的大晶粒钙钛矿且同时提升转换效率与稳定性。围绕目标针对富碘配体/极性富勒烯复合材料，作为钙钛矿晶体成长的异质晶核，提升晶体的结晶性与形貌。通过项目实施，将晶体成长、薄膜性质和器件性能多方面掌握富碘配体对器件影响的内在本质，澄清工作机制。为钙钛矿的晶体生长提供理论指导，进而为器件性能的优化提供新的思路。..主要研究内容分为下列两个部分:..（一）使用低温溶液制备极性富勒烯(C60 pyrrolidine tris-acid，CPTA)电子传输层。通过CPTA与氧化铟锡导电玻璃(ITO)表面的酯化反应，形成均匀、致密且能带匹配的电子传输层，进一步可用于制备无迟滞、可弯曲和稳定的钙钛矿太阳能电池。因此，CPTA有希望替代以金属氧化物为主的电子传输层，同时也有利于应用在其他便携式光伏器【Adv. Energy Mater. 2017, 7, 1701144; Adv. Sci. 2018, 5, 1800159; J. Mater. Chem. C 2018, 6, 6982; ACS Appl. Mater. Inter. 2018, 10, 14986; Org. Electron. 2017, 48, 204】；..（二）碘化铅(PbI2)作为富碘材料的前躯体，经过与其他材料的共价键结可形成CH3HN3PbI3型钙钛矿的晶核([PbI6]4-)。利用CPTA与PbI2发生强的配位作用，预先形成可控制数量的[PbI6]4-界面型晶核。进一步通过成核密度的设计，可提升钙钛矿晶粒的结晶性，同时晶胞成长至1微米。一方面，光生载流子的数量可提升；另一方面，晶界的减少将可减少载流子复合。因此，在太阳能电池上，可达到超过20%的光电转换效率与超过80%的填充因子【Adv. Funct. Mater. 2018, 28, 1706317】。

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