TPD wide-bandgap polymers for solar cell application and their sensitization with small molecule dyes

In this paper we report about some TPD (triphenylamine dimer: N,N′-diphenyl-bis(4-methylphenyl)-biphenyl-4,4′-diamine) polymers, which differ in the kind of conjugation and co-monomer to proof their potential as transparent polymer solar cell (PSC) materials and to check their ability to be sensitized with dyes which can be useful for application niches and for use as optical/UV sensors with narrow-band spectral response, respectively. The wide-bandgap Poly-TPD was found to be suitable in non-sensitized form with light power conversion efficiency of 0.4% in PSC only blended with PCBM. Further investigations were performed employing PSCs with the bright yellow PPV derivative (TPD-MEH-PPV) and the non-conjugated colorless polymer (Poly-TPD-DPX); their efficiencies could be doubled by coloration with certain small molecule dyes. These were applied as photoactive materials up to a dye:polymer composition of 4:1. The polymer serves as a film-forming matrix and their TPD-units ensure hole-transport. The open-circuit voltages (Voc) increased from non-sensitized to sensitized PSC, due to the more favorable energy levels of the dyes as one explanation.