New polythiophene derivatives and enhanced photovoltaic effect by a boron compound blended with them in OPVs cells

• New polythiophene derivatives and their use in organic photovoltaic (OPV) devices.
• Two fold improved in OPVs cells efficiency when doped with an organo-boron compound.
• HOMO–LUMO levels and correlation with absorption and device photovoltaic performance.

Synthesis and characterization of new polythiophenes derivatives PI, PC, PD, and PA are presented; the synthesis method to obtain such polymers is easy of performing, inexpensive, versatile and reproducible. Experimental measurements of the HOMO and LUMO levels, electrochemically determined, of these polymers are also reported and their energy gaps are correlated with their absorption spectra and the device photovoltaic performance. When in the active layer of solar cells are mixed any of these polymers with the organo-boron compound 6-nitro-3-(E)-3-(4-dimethylaminophenyl)allylidene)-2,3-dihydrobenzo[d]-[1,3,2]-oxazaborole (M1), more than two fold improved power conversion efficiency is reached. M1 presents a red shift absorption band with respect to those of the new synthesized polythiophene derivatives, increasing the overall absorption when blending with these polymers, and due to also its electron donor character, there exists an enhanced efficiency. The solar performance of these OPVs cells was acceptable with an average Voc of above 500 mV, a Jsc of almost 3 mA/cm2, and η = 0.41%.