Ab Initio Study of a Molecular Crystal for Photovoltaics: Light Absorption, Exciton and Charge Carrier Transport

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• 作者：Andriy Zhugayevych ; Olena Postupna ; Ronald C. Bakus II ; Gregory C. Welch ; Guillermo C. Bazan ; Sergei Tretiak
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：March 14, 2013
• 年：2013
• 卷：117
• 期：10
• 页码：4920-4930
• 全文大小：596K
• 年卷期：v.117,no.10(March 14, 2013)
• ISSN：1932-7455

文摘

Using ab initio methods we examine the molecular and solid-state electronic properties of a recently synthesized small-molecule donor, p-DTS(PTTh₂)₂, which belongs to the dithienosilole-pyridylthiadiazole family of chromophores. In combination with the PC₇₀BM acceptor, p-DTS(PTTh₂)₂ can be used to fabricate high-efficiency bulk heterojunction organic solar cells. A precise picture of molecular structure and interchromophore packing is provided via a single-crystal X-ray diffraction study; such details cannot be easily obtained with donor materials based on conjugated polymers. In first-principles approaches we are limited to a single-crystallite scale. At this scale, according to our investigation, the principal properties responsible for the high efficiency are strong low-energy light absorption by individual molecules, large exciton diffusion length, and fast disorder-resistant hole transport along 蟺-stacks in the crystallite. The calculated exciton diffusion length is substantially larger than the average crystallite size in previously characterized device active layers, and the calculated hole mobility is 2 orders of magnitude higher than the measured device-scale mobility, meaning that the power conversion 鈥渓osses鈥?on a single-crystallite scale are minimal.