Improvement of the photovoltaic properties for P3HT:PCBM system annealed at the temperature in liquid crystalline regions induced by liquid crystal molecules

Abstract

The poly(3-hexylthiophene):[6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction organic photovoltaics (BHJ OPVs) showed a maximum value of 3.5 % by incorporating of 6 wt% nematic liquid crystals (NLCs) of 4-octyloxy-4 0 -cyanobiphenyls (8OCB) after annealing at the temperature of 70°C in liquid crystalline transitions. The 8OCB was immiscible with P3HT, and the melting temperature of P3HT was not influenced at 8OCB doping amount below 10 wt%. Based on the UV-vis analysis, the conjugation length and chain order of P3HT should be the highest at 8OCB content of 6 wt% after annealing at 70°C. The reflection peak of P3HT shifted to lower positions as the annealing temperature increasing from 70 to 130°C, indicating that PCBM and 8OCB molecules could be incorporated into the lamellar spacing of P3HT crystallites at high annealing temperatures. The improvement of the solar cell device after annealing at 70°C is probably due to the optimized phase separation morphology and relatively higher hole mobility in P3HT:PCBM:8OCB system. The 8OCB molecules in the liquid crystalline state are supposed to be a good template for the crystallization of P3HT, as well as the phase separation between P3HT and PCBM.

Enhancement of inverted organic solar cell parameters by post-production annealing process

“…A mixture of commercially purchased Poly(3-hexylthiophene-2,5-diyl) (P3HT) (Sigma-Aldrich, number average molecular weight (M w : 45 000-65 000 g mol −1 and polydispersity index of ∼2, (CAS Number: 156074-98-5)) and [6,6]-PCBM (Sigma-Aldrich, CAS Number: 160848-22-6) (1:1 wt-ratio) were diluted in 20 mg ml −1 solvent of dichlorobenzene (Sigma-Aldrich, CAS Number: 108-90-7) with a magnetic stirrer at temperature of 40 • C for 24 h. Then, the diluted polymer mixture of P3HT:PCBM was spin coated on top of the Glass/ITO/ZnO substrates with 600 RPM for 20 s followed by 1100 RPM for 9 s at room temperature. The thickness of P3HT:PCBM photoactive layer was measured to be between 130 and 140 nm.…”

“…After drying the solvent by applying heat treatment, the donor conjugated polymer and the acceptor fullerene create charge-separating heterojunctions in the nanoscale across the photoactive layer [1]. The most commonly examined polymer blended system is based on a solutiontreated and mixture of poly (3-hexyl-thiophene) (P3HT) as a p-type semiconducting conjugated polymer and [6,6]-phenyl C61butyric acid methyl ester (PCBM) as an n-type fullerene [4]. This polymer blending system (P3HT:PCBM) has been reported to have different device efficiency values in between 2% and 5% depending on the fabrication conditions [5][6][7].…”

“…The most commonly examined polymer blended system is based on a solutiontreated and mixture of poly (3-hexyl-thiophene) (P3HT) as a p-type semiconducting conjugated polymer and [6,6]-phenyl C61butyric acid methyl ester (PCBM) as an n-type fullerene [4]. This polymer blending system (P3HT:PCBM) has been reported to have different device efficiency values in between 2% and 5% depending on the fabrication conditions [5][6][7]. The performance of polymer based organic solar cells generally depends on the effectiveness of excitons produced in the photoactive polymer layers, and their separation into free electrons and holes [8].…”

Liquid crystals in photovoltaics: a new generation of organic photovoltaics

“…[155][156][157][158] Canli et al 155 investigated the effect of a chiral smectic LC namely (S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino}-methyl]-phenol 27a (Figure 23) in a P3HT/PCBM BHJ organic solar cell. The charge-carrier mobility of the composites increased on addition of the LC material.…”