Esterification of Indoline-Based Small-Molecule Donors for Efficient Co-evaporated Organic Photovoltaics

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• 作者：Zhongqiang Wang ; Xiao-Feng Wang ; Daisuke Yokoyama ; Hisahiro Sasabe ; Junji Kido ; Zhaoyang Liu ; Wenjing Tian ; Osamu Kitao ; Toshitaka Ikeuchi ; Shin-ichi Sasaki
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：July 10, 2014
• 年：2014
• 卷：118
• 期：27
• 页码：14785-14794
• 全文大小：477K
• ISSN：1932-7455

文摘

In this study, we attempted to develop a protocol for fabricating efficient solid-state organic photovoltaics based on materials used currently for dye-sensitized solar cells. Three typical indoline dyes, namely, D131, D102, and D149, were employed as electron donors in conjunction with C₇₀ fullerene in solution-processed planar-heterojunction (PHJ) organic solar cells (OSCs). The PHJ cells based on these dyes exhibited similar external quantum efficiencies over the entire spectral range, resulting in identical short-circuit photocurrents. The open-circuit voltages of the PHJ cells were consistent with the highest occupied molecular orbital level of the corresponding indoline dye. The D102-based PHJ cell exhibited the highest power conversion efficiency, of up to 3.1%. The efficiency was limited by the light-harvesting capability of the solar cell, given that the short diffusion length (5 nm) of D102 limited the thickness of the active layer; the diffusion length was determined through an optical simulation. The methyl ester of D102 (D102-Me) was synthesized to reduce the degree of intermolecular hydrogen bonding between the dye molecules. D102-Me was found to be more suited for use in OSCs fabricated by the thermal evaporation method. PHJ cells based on solution-processed and thermally evaporated active layers of D102-Me exhibited similar photovoltaic performances. However, in the case of D102, the device with the thermally evaporated layer exhibited lower performance than that of the device with the solution-processed layer, owing to the decomposition of D102 during the evaporation process. D102-Me was then co-evaporated with C₇₀ in bulk-heterojunction OSCs. A power conversion efficiency as high as 5.1% could be achieved by optimizing this active layer; the D102-Me/C₇₀ blend ratio in the optimized layer was 1:9, and the thickness of the layer was 70 nm.