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Manipulating Backbone Structure to Enhance Low Band Gap Polymer Photovoltaic Performance
Author(s) -
Huang Ye,
Liu Feng,
Guo Xia,
Zhang Wei,
Gu Yu,
Zhang Jianping,
Han Charles C.,
Russell Thomas P.,
Hou Jianhui
Publication year - 2013
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201300031
Subject(s) - materials science , polymer solar cell , energy conversion efficiency , band gap , polymer , organic solar cell , density functional theory , absorption (acoustics) , absorption spectroscopy , chemical physics , solar cell , optoelectronics , analytical chemistry (journal) , optics , organic chemistry , computational chemistry , chemistry , physics , composite material
A pair of polymers, PBDTBT and PBDTDTBT , was synthesized for application in polymer solar cells (PSCs). Although these two polymers have similar absorption bands and molecular energy levels, PBDTDTBT exhibits much better photovoltaic performance in polymer solar cell (PSC) devices with power conversion efficiency (PCE) of 7.4%. To understand the differences between PBDTDTBT and PBDTBT , we have investigated the correlations of the molecular structure, morphology, dynamics and efficiency of these two polymers. A theoretical investigation using density functional theory (DFT) and time‐dependent DFT (TDDFT) has been employed to investigate the electron density and electron delocalization extent of the unimers. TEM data showed that PBDTDTBT phase separates from PC 71 BM, while PBDTBT suffers from having a proper morphology on different processing conditions. Grazing incidence wide angle X‐ray diffraction (GIWAXD) was used to probe the crystal structure of the polymers in thin film. A polymorph crystal structure was observed for PBDTBT . Grazing incidence small angle X‐ray scattering (GISAXS) was used to probe the size scale of phase separation, with an optimized 25 nm feature size observed for PBDTDTBT /PC 71 BM blends, which agrees well with TEM results. Femtosecond transient absorption (TA) spectroscopy was used to probe the dynamics of the fundamental processes in organic photovoltaic (OPV) materials, such as charge separation and recombination. The enhanced absorption coefficient, good charge separation, optimal phase separation and higher charge mobility all contribute to the high PCE of the PBDTDTBT /PC 71 BM devices.