Sharma Amit, Singh Ranbir, Kini Gururaj P, Hyeon Kim Ji, Parashar Mritunjaya, Kim Min, Kumar Manish, Kim Jong Seung, Lee Jae-Joon
Department of Chemistry, Korea University, Seoul 02841, Republic of Korea.
Council of Scientific & Industrial Research-Central Scientific Instruments Organisation (CSIR-CSIO), Sector 30, Chandigarh 160030, India.
ACS Appl Mater Interfaces. 2021 Feb 17;13(6):7405-7415. doi: 10.1021/acsami.0c17583. Epub 2021 Feb 3.
The design and synthesis of a stable and efficient hole-transport material (HTM) for perovskite solar cells (PSCs) are one of the most demanding research areas. At present, 2,2',7,7'-tetrakis[,-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-MeOTAD) is a commonly used HTM in the fabrication of high-efficiency PSCs; however, its complicated synthesis, addition of a dopant in order to realize the best efficiency, and high cost are major challenges for the further development of PSCs. Herein, various diketopyrrolopyrrole-based small molecules were synthesized with the same backbone but distinct alkyl side-chain substituents (i.e., 2-ethylhexyl-, -hexyl-, ((methoxyethoxy)ethoxy)ethyl-, and (2-((2-methoxyethoxy)ethoxy)ethyl)acetamide, designated as D-1, D-2, D-3, and D-4, respectively) as HTMs. The variation in the alkyl chain has shown obvious effects on the optical and electrochemical properties as well as on the molecular packing and film-forming ability. Consequently, the power conversion efficiency (PCE) of the PSC under one sun illumination (100 mW cm) is shown to increase in the order of D-1 (8.32%) < D-2 (11.12%) < D-3 (12.05%) < D-4 (17.64%). Various characterization techniques reveal that the superior performance of D-4 can be ascribed to the well-aligned highest occupied molecular orbital energy level with the counter electrode, the more compact π-π stacking with a higher coherence length, and the excellent hole mobility of 1.09 × 10 cm V s, thus providing excellent energetics for effective charge transport with minimal charge-carrier recombination. Furthermore, the addition of the dopant Li-TFSI in D-4 is shown to deliver a remarkable PCE of 20.19%, along with a short-circuit current density (), open-circuit voltage (), and fill factor (FF) of 22.94 mA cm, 1.14 V, and 73.87%, respectively, and superior stability compared to that of other HTMs. These results demonstrate the effectiveness of side-chain engineering for tailoring the properties of HTMs, thus offering new design tactics to fabricate for the synthesis of highly efficient and stable HTMs for PSCs.
设计并合成一种用于钙钛矿太阳能电池（PSC）的稳定且高效的空穴传输材料（HTM）是最具挑战性的研究领域之一。目前，2,2',7,7'-四[,-二(4-甲氧基苯基)氨基]-9,9'-螺二芴（螺-甲基三苯胺，spiro-MeOTAD）是制造高效PSC时常用的HTM；然而，其合成复杂、为实现最佳效率需添加掺杂剂以及成本高昂，是PSC进一步发展的主要挑战。在此，合成了各种基于二酮吡咯并吡咯的小分子，它们具有相同的主链但不同的烷基侧链取代基（即2-乙基己基-、-己基-、((甲氧基乙氧基)乙氧基)乙基-和(2-((2-甲氧基乙氧基)乙氧基)乙基)乙酰胺，分别命名为D-1、D-2、D-3和D-4）作为HTM。烷基链的变化对光学和电化学性质以及分子堆积和成膜能力都有明显影响。因此显示，在一个太阳光照（100 mW/cm²）下PSC的功率转换效率（PCE）按D-1（8.32%）< D-2（11.12%）< D-3（12.05%）< D-4（17.64%）的顺序增加。各种表征技术表明，D-4的优异性能可归因于其与对电极的最高占据分子轨道能级良好对齐、具有更高相干长度的更紧密π-π堆积以及1.09×10⁻³ cm² V⁻¹ s⁻¹的优异空穴迁移率，从而为有效电荷传输提供了优异的能量学条件，且电荷载流子复合最少。此外，在D-4中添加掺杂剂双(三氟甲基磺酰)亚胺锂（Li-TFSI）显示出20.19%的显著PCE，以及分别为22.94 mA/cm²、1.14 V和73.87%的短路电流密度（Jsc）、开路电压（Voc）和填充因子（FF），并且与其他HTM相比具有优异的稳定性。这些结果证明了侧链工程在调整HTM性质方面的有效性，从而为合成用于PSC的高效且稳定的HTM提供了新的设计策略。
