A thienylenevinylene-phthalimide copolymer based polymer solar cell with high open circuit voltage: Effect of additive concentration on the open circuit voltage

• We report alkyl-substituted thienylenevinylene and phthalimide copolymer-based polymer solar cells (PSCs).
• This polymer based PSCs showed a high open circuit voltage (Voc) of 0.87 V due to lower HOMO levels.
• The photovoltaic properties of this PSC significantly depended on concentration of the solvent additives.
• In particular, the Voc in PTVPhI-Eh-based PSCs was significantly affected.
• We investigated the relationship between Voc and concentration of various solvent additives using various analyses.

Polymer solar cells (PSCs) based on alkyl-substituted thienylenevinylene and phthalimide-based D-A copolymer (PTVPhI-Eh) as a donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor were investigated with the intent of gaining high performance photovoltaic properties. PTVPhI-Eh had a deep highest-occupied molecular orbital (HOMO) level, ~0.3 eV lower than rr-P3HT. As a result, PTVPhI-Eh:PC71BM devices showed a high open circuit voltage (Voc) of 0.87 V, which is over 0.2 V higher compared to that of P3HT:PCBM-based PSCs. The maximum power conversion efficiency (PCE) of PSCs was 4.14% with Voc of 0.87 V, short circuit current (Jsc) of 7.32 mA/cm2, and fill factor (FF) of 65%, under optimized conditions of a 1:1 wt/wt ratio and treatment with a 2 vol% 1-chloronaphthalene solvent additive. The Voc and consequent photovoltaic performance of this PSC was significantly affected by the concentration of the solvent additive. To determine the relationship between Voc and concentration of solvent additive, PTVPhI-Eh:PC71BM devices were investigated with various analyses such as optical spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD).

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