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Title: Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors

The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here in this paper, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh 2) 2, namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. Lastly, in polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregationmore » and charge percolation to the electrodes.« less
Authors:
 [1] ;  [2] ;  [2] ;  [3] ;  [1] ;  [2] ;  [4] ;  [2] ;  [1] ;  [5] ;  [6] ;  [5] ;  [5] ;  [4] ;  [3] ;  [2] ;  [7] ; ORCiD logo [1]
  1. Washington State Univ., Pullman, WA (United States). Dept. Physics and Astronomy
  2. King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudia Arabia). KAUST Solar Center, Physical Sciences and Engineering Division, Material Science and Engineering Program
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  4. Univ. of Potsdam, Postsdam (Germany). Inst. fur Physik und Astronomie, Physik weicher Materie
  5. Univ. of Queensland, Brisbane (Australia). Centre for Organic Photonics & Electronics
  6. King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudia Arabia). KAUST Solar Center, Physical Sciences and Engineering Division (PSE), Chemical Sciences Program
  7. King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudia Arabia). KAUST Solar Center, Physical Sciences and Engineering Division (PSE), Chemical Sciences Program; King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudia Arabia). KAUST Solar Center, Physical Sciences and Engineering Division, Material Science and Engineering Program
Publication Date:
Grant/Contract Number:
AC02-05CH11231; CRG_R2_13_BEAU_KAUST_1; DP120101372; AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Advanced Energy Materials
Additional Journal Information:
Journal Volume: 8; Journal Issue: 19; Journal ID: ISSN 1614-6832
Publisher:
Wiley
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; 36 MATERIALS SCIENCE; Small molecule; organic solar cell; photovoltaic device; charge transport; domain purity; mixed domains; resonant X-ray scattering; microscopy; transient spectroscopy
OSTI Identifier:
1462361
Alternate Identifier(s):
OSTI ID: 1429523