Ramona Gironda, Jinwoo Choi, L. Miozzo
Jun 18, 2012
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Journal
Synthetic Metals
Abstract
Abstract The synthesis of a novel electron-deficient derivatives of pyrrolo[3,4-c]pyrrole-1,4 (2H,5H)-dione, (DPP), 1,4-bis-(4-butyl-phenyl)-3,6-di-thiophen-2-yl-pyrrolo[3,2-b]pyrrole-2,5 – (1H,4H)-dione and 1,4-bis-(4-(pentyloxy)phenyl)-3,6-bis(thiophen-2-yl-pyrrolo[3,2-b]pyrrole-2,5-(1H,4H)-dione are reported. This new building block was copolymerized with bistannanes of thiophene and bithiophene and fluorene by using Stille or Suzuki polymerization, affording the corresponding copolymers ( P1 – P4 , respectively). These exhibit small energy band gaps combined with low-lying HOMO energy levels. Energy band gaps of P1 and P2 , calculated from absorption spectra, are 1.63 and 1.73 eV, respectively. The HOMO and LUMO energy levels of P1 and P2 are −5.12, −3.50, −5.09 and −3.50 eV respectively, as determined by cyclic voltammetry. The power conversion efficiency of P1:PC 61 BM-based photovoltaic cells illuminated by AM 1.5G was 1.24%, without optimization of materials, significantly higher than for P2 :PC 61 BM, 0.33%. These results demonstrate that thiophene-pyrrolo[3,2-b]pyrrole-2,5-dione conjugated copolymers are promising materials for bulk heterojunction solar cell applications.