Small Molecular Hole-Transporting Materials for Efficient Inverted Perovskite Solar Cells

Hybrid Organic-Inorganic perovskite solar cells (PVSCs) are a new type of thin-film solar cells based on inorganic-organic hybrid metal halide active materials. Perovskites show many distinctive advantages, such as strong light absorption, small exciton binding energy, adjustable optical band gap, high charge carrier mobility, long charge carrier lifetime, and solution processability. Therefore, PVSCs, with perovskite as the light absorption layer, exhibit excellent photovoltaics performance. The inverted PVSCs can form films at low temperatures and lower the production cost, providing the possibility for the commercial development of flexible devices. High-mobility charge transport layers can improve exciton separation and reduce carrier recombination, which is essential to obtain highly efficient PVSCs. Small molecular HTMs (SM-HTMs) have a well-defined molecular structure and molecular weight, and there is negligible batch-to-batch variation, so the device performance has better reproducibility. In this thesis, the design of SM-HTM, as well as their high-efficiency devices, are discussed by studying three high-efficiency PVSC systems. Firstly, three isomeric HTMs based on distinct dithienothiophene π-bridge were synthesized, suggesting that a small change of the regioisomeric π-bridge structure of D-π-D typed molecules can greatly alter their photophysical properties. A power conversion efficiency (PCE) of 19.23% was achieved with 3T-3. Secondly, a green-solvent-processable hole-transport material M1 enabled by a traditional bidentate ligand 1,10-phenanthroline was synthesized and showed effective perovskite surface passivation, achieving a high PCE of 20.14%. Thirdly, a D-A-D type hole-transport material TPA-FO features an inexpensive aromatic ketone, 9-fluorenone as the core, and enables inverted perovskite solar cells with an efficiency of 20.24%. Our results suggest that constructing SM-HTMs with versatile conjugated planar cores like polythiophenes, 1,10-phenanthroline, and aromatic ketones shows the potential to develop the low-cost, ecofriendly-processable HTMs toward highly efficient PVSCs and give some insight into the structure-property relationship of SM-HTMs.

有机-无机杂化钙钛矿太阳能电池（PVSCs）是一种基于无机-有机混合金属卤化物活性层的新型薄膜太阳能电池。钙钛矿显示出许多独特的优势，如吸光强度高、激子结合能小、可调光学带隙、高电荷载流子迁移率、长电荷载流子寿命和溶液可加工性。因此，以钙钛矿为光吸收层的 PVSCs 表现出优异的光伏性能。倒置的PVSCs可以在低温下成膜，降低生产成本，为柔性器件的商业开发提供了可能。高迁移率电荷传输层可以改善激子分离并减少载流子复合，这对于获得高效 PVSC 至关重要。小分子空穴传输材料 (SM-HTMs) 具有明确的分子结构和分子量，批次间的差异可以忽略不计，因此器件性能具有更好的重现性。本论文通过对三种高效PVSC系统的研究，讨论了SM-HTM及其高效器件的设计。首先，合成了三种基于不同双噻吩并噻吩 π 桥的异构 HTM，表明 D-π-D 型分子的区域异构 π 桥结构的微小变化可以极大地改变它们的光物理性质。 3T-3 实现了 19.23% 的光电转换效率 (PCE)。其次，合成了一种由传统双齿配体 1,10-菲咯啉实现的绿色溶剂可加工空穴传输材料 M1，该材料显示出有效的钙钛矿表面钝化，实现了 20.14% 的高 PCE。第三，D-A-D型空穴传输材料TPA-FO以廉价的芳香酮9-芴酮为核心，实现了效率为20.24%的倒置钙钛矿太阳能电池。我们的结果表明，构建具有多功能共轭平面核（如聚噻吩、1,10-菲咯啉和芳香酮）的 SM-HTM 显示出开发低成本、环保可加工 HTM 以实现高效 PVSC 的潜力，并研究了 SM-HTMs的构效关系。