Improvement in carrier mobility and photovoltaic performance through random distribution of segments of linear and branched side chains

Abstract

The random distribution of segments of linear octyloxy side chains and of branched 2-ethylhexyloxy side chains, on the backbone of anthracene containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) has resulted in a side chain based statistical copolymer, denoted AnE-PVstat, showing optimized features as compared to the well defined homologues whose constitutional units are incorporated into its backbone. Electric field independent charge carrier mobility (µ_hole) for AnE-PVstat was demonstrated by CELIV and OFET measurements, both methods resulting in similar µ_hole values of up to 5.43 × 10⁻⁴ cm² V⁻¹ s⁻¹. Upon comparison, our results show that charge carrier mobility as measured by CELIV technique is predominantly an intrachain process and less an interchain one, which is in line with past photoconductivity results from PPE-PPV based materials. The present side chain distribution favors efficient solar cell active layer phase separation. As a result, a smaller amount of PC₆₀BM is needed to achieve relatively high energy conversion efficiencies above 3%. The efficiency of η_AM1.5 ≈ 3.8% obtained for AnE-PVstat:PC₆₀BM blend is presently the state-of-art value for PPV-based materials.