High open-circuit voltage poly(ethynylene bithienylene):: Fullerene solar cells

The synthesis to improve then open circuit voltage of P3HT:PCBM bulk heterojunction photovoltaic cells was investigated. The open circuit voltages was between 0.8 and 1.05 V as a result of their lower HOMO levels. When the HOMO levels was lowered the optical band gap maintained the LUMO level shifts correspondingly and care must be taken. PEBT was synthesized through a palladium catalyzed Shonogashira polymerization providing molecular weights. The absorption spectra of PEBT and P3HT exhibit partly resolved vibrational fine structure and show a significant red shift that is due to the planarization of the π-system and interchain interactions induced by the aggregation and crystallization. Photovoltaic cells were made by spin coating mixtures of PEBT and PCBM in different weight ratios from chlorobenzene solution on prepatterned ITO. It was observed that EQE in the wavelength ranges between 400 and 550 nm and devices with 1:4 blend of PEBT and PCBM exhibit EQE of 42%.