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Title: Open-Circuit Voltage Losses in Selenium-Substituted Organic Photovoltaic Devices from Increased Density of Charge-Transfer States

Using an analysis based on Marcus theory, we characterize losses in open-circuit voltage (V OC) due to changes in charge-transfer state energy, electronic coupling, and spatial density of charge-transfer states in a series of polymer/fullerene solar cells. Here, we use a series of indacenodithiophene polymers and their selenium-substituted analogs as electron donor materials and fullerenes as the acceptors. By combining device measurements and spectroscopic studies (including subgap photocurrent, electroluminescence, and, importantly, time-resolved photoluminescence of the charge-transfer state) we are able to isolate the values for electronic coupling and the density of charge-transfer states (NCT), rather than the more commonly measured product of these values. We find values for NCT that are surprisingly large (~4.5 × 10 21–6.2 × 10 22 cm -3), and we find that a significant increase in N CT upon selenium substitution in donor polymers correlates with lower VOC for bulk heterojunction photovoltaic devices. The increase in N CT upon selenium substitution is also consistent with nanoscale morphological characterization. Using transmission electron microscopy, selected area electron diffraction, and grazing incidence wide-angle X-ray scattering, we find evidence of more intermixed polymer and fullerene domains in the selenophene blends, which have higher densities of polymer/fullerene interfacial charge-transfer states. Ourmore » results provide an important step toward understanding the spatial nature of charge-transfer states and their effect on the open-circuit voltage of polymer/fullerene solar cells« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [4] ;  [6] ;  [6] ;  [6] ;  [1] ;  [4] ;  [1]
  1. Univ. of Washington, Seattle, WA (United States). Dept. of Chemistry
  2. Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering; Inst. of Photovoltaics, Nanchang (China)
  3. Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering; Univ. of Wisconsin, Green Bay, WI (United States). Dept. of Natural and Applied Sciences
  4. Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering
  5. Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering; Zhejiang Univ., Hangzhou (China). Dept. of Polymer Science and Engineering
  6. Univ. of Washington, Seattle, WA (United States). Dept. of Chemical Engineering
Publication Date:
Grant/Contract Number:
SC0005153
Type:
Published Article
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 27; Journal Issue: 19; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
Univ. of Washington, Seattle, WA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1215764
Alternate Identifier(s):
OSTI ID: 1436293