Synthesis and Characterization of Polymers based on Benzimidazole Segments for Polymer Solar Cells

Abstract

To enhance performance of polymer solar cells, a series of polymers which were based on electron-deficient benzimidazole segments and electron-rich benzodithiophene segments for polymer solar cells were designed and synthesized by the Stille polycondensation. The synthesized polymers which had long alkyl side chain exhibited good solubility in organic solvents. The optical and electrochemical properties of polymers were measured by UV/Vis spectroscopy and cyclic voltammetry (CV). The resulting polymers exhibited low optical bandgaps and electrochemical bandgaps. Furthermore, HOMO and LUMO energy levels of -3.4 ~ 6.0 eV were suitable for photovoltaic applications. These HOMO and LUMO energy levels are appropriate for charge transport to achieve high performance of polymer solar cells. The optical and electrochemical properties were tuned by introducing different substituents and alkyl side chains on benzimidazole segments. The polymer solar cells with benzimidazole based polymer achieved power conversion efficiency close to 1% due to their enhanced light harvesting property and efficient interpenetrating network which were caused by a hydrogen atom on benzimidazole segment and a lack of long alkyl side chain. This work implies that the electron-deficient benzimidazole segments based polymers can achieve high PCE through structural modification of the polymer. ⓒ 2013 DGIST