Unified assay of adverse effects from the varied nanoparticle hybrid in polymer–fullerene organic photovoltaics

Abstract

Nanoparticles (NPs) having different surface capping agent, variant electrical conductivity and sunlight absorption have been studied for the ternary hybrid containing poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) in bulk heterojunction (BHJ) organic photovoltaics (OPVs). These NPs are composed of conducting gold, semiconducting CdS or PbS, or insulating cage-like molecular silica (POSS). We use a series of microscopic methods including TEM, AFM, SEM, optical, and fluorescence microscopy to estimate NP size and to probe the agglomeration and/or aggregation of NPs in P3HT/PCBM blends. Surface capping agent aromatic thiophenol (SPh) was found to be poor in the dispersion of NPs in P3HT/PCBM blends. The light harvesting of these NPs ranges from transparent (POSS NP), near transparent (CdS NP), visible light absorbing (Au NP), to near-infrared absorbing (PbS NP). Nevertheless, the absorbance of these NPs is all too small relative to that of P3HT polymer. Concerning the charge separation of P3HT exciton, the LUMO energy levels of these NPs have been determined by the combination of optical band-gap energy and HOMO energy levels. By the transient photocurrent time-of-flight method, charge carrier mobility of P3HT/PCBM/NP(CdS-SPh) ternary hybrid was found to be improved, although fluorescence quenching studies imply insufficient or ineffective contact between P3HT and all NPs in the present study. NPs hybrid P3HT/PCBM BHJ OPVs were fabricated by solution process. Regardless of conductivity or sunlight absorbance, all NPs show no improvement on power conversion efficiency of ternary hybrid OPVs, which is 3.03–3.91% less than 4.0–4.1% of P3HT/PCBM OPVs without NPs. Based on the present study, a few problems that associate with the inferior performance of NPs hybrid P3HT/PCBM BHJ OPVs are delineated.