Opto-Electrical Properties of Composite Materials Based on Two Benzotrithiophene Copolymers and Fullerene Derivatives

Two donor–acceptor copolymers based on a benzotrithiophene acceptor unit and an electron-donor segment of 4,8-didodecyloxybenzo[1,2-b;4,5-b′]dithiophene were investigated in the view of photovoltaic application. We provided the complete synthesis procedure supported with NMR spectra of the monomers obtained. The resulting copolymers, labeled P1 and P2 in this work, exhibit strong absorption in the visible region with a similar band gap of about 2.2 eV. In spite of the chemical similarity of both copolymers, the photovoltaic and carrier transport properties of the P1- and P2-based devices demonstrated a noticeable difference. Applying an optimization procedure, a power conversion efficiency of 4.6% has been achieved for the P2/PC71BM solar cells