期刊
NANOSCALE
卷 7, 期 38, 页码 15576-15583出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c5nr03332b
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资金
- U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division
- U.S. Department of Energy (DOE) by Argonne National Laboratory [DE-AC02-06CH11357]
- Scientific User Facilities Division, U.S. Department of Energy
Advances in material design and device engineering led to inverted organic solar cells (i-OSCs) with superior power conversion efficiencies (PCEs) compared to their conventional counterparts, in addition to the well-known better ambient stability. Here, we report an in-depth morphology study of the i-OSC active and cathode modifying layers, employing a model system with a well-established bulk-heterojunction, PTB7:PC71BM as the active layer and poly-[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt- 2,7-(9,9-dioctylfluorene)] (PFN) as the cathode surface modifying layer. We have also identified the role of a processing additive, 1,8-diiodooctane (DIO), used in the spin-casting of the active layer to increase PCE. Using various characterization techniques, we demonstrate that the high PCEs of i-OSCs are due to the diffusion of electron-accepting PC71BM into the PFN layer, resulting in improved electron transport. The diffusion occurs when residual solvent molecules in the spun-cast film act as a plasticizer. Addition of DIO to the casting solution results in more PC71BM diffusion and therefore more efficient electron transport. This work provides important insight and guidance to further enhancement of i-OSC performance by materials and interface engineering.
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