Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells

Herath, Nuradhika; Das, Sanjib; Keum, Jong K.; Zhu, Jiahua; Kumar, Rajeev; Ivanov, Ilia N.; Sumpter, Bobby G.; Browning, James F.; Xiao, Kai; Gu, Gong; Joshi, Pooran; Smith, Sean; Lauter, Valeria

doi:10.1038/srep13407

Title: Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells

Journal Article · Fri Aug 28 00:00:00 EDT 2015 · Scientific Reports

DOI:https://doi.org/10.1038/srep13407· OSTI ID:1259703

Herath, Nuradhika ^[1]; Das, Sanjib ^[2]; Keum, Jong K. ^[1]; Zhu, Jiahua ^[1]; Kumar, Rajeev ^[1]; Ivanov, Ilia N. ^[1]; Sumpter, Bobby G. ^[1]; Browning, James F. ^[1]; Xiao, Kai ^[1]; Gu, Gong ^[2]; Joshi, Pooran ^[1]; Smith, Sean ^[3]; Lauter, Valeria ^[1]

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Univ. of Tennessee, Knoxville, TN (United States)
UNSW Australia, Sydney, NSW (Australia)

Structural characteristics of the active layers in organic photovoltaic (OPV) devices play a critical role in charge generation, separation and transport. Here we report on morphology and structural control of p-DTS(FBTTh₂)₂:PC₇₁BM films by means of thermal annealing and 1,8-diiodooctane (DIO) solvent additive processing, and correlate it to the device performance. By combining surface imaging with nanoscale depth-sensitive neutron reflectometry (NR) and X-ray diffraction, three-dimensional morphologies of the films are reconstituted with information extending length scales from nanometers to microns. DIO promotes the formation of a well-mixed donor-acceptor vertical phase morphology with a large population of small p-DTS(FBTTh₂)₂ nanocrystals arranged in an elongated domain network of the film, thereby enhancing the device performance. In contrast, films without DIO exhibit three-sublayer vertical phase morphology with phase separation in agglomerated domains. Our findings are supported by thermodynamic description based on the Flory-Huggins theory with quantitative evaluation of pairwise interaction parameters that explain the morphological changes resulting from thermal and solvent treatments. Our study reveals that vertical phase morphology of small-molecule based OPVs is significantly different from polymer-based systems. In conclusion, the significant enhancement of morphology and information obtained from theoretical modeling may aid in developing an optimized morphology to enhance device performance for OPVs.

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Research Organization:: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: AC05-00OR22725

OSTI ID:: 1259703

Alternate ID(s):: OSTI ID: 1333656

Journal Information:: Scientific Reports, Vol. 5; ISSN 2045-2322

Publisher:: Nature Publishing GroupCopyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 16 works

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Title: Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells

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