Optimization of hybrid P3HT:CdSe photovoltaic devices through surface ligand modification

Abstract

Within the last few years, renewable energy devices have been gaining growing interest and the quest for environmentally friendly efficient photovoltaic cells continues. Amongst commonly used designs, bulk heterojunctions consist of blending a conjugated polymer donor with semiconducting nanocrystals (NCs) as acceptors. These nanocrystals are promising substitutes for fullerene normally used as acceptor, offering better electron mobility, tunable band gap and higher dielectric constant to prevent recombination of charge carrier into excitons. In this work, cadmium selenide nanocrystals (CdSe) capped with different phosphine oxides (R3PO: R = Me2N, Et2N, pyrrolidinyl (Pyrr), piperidinyl (Pip) or octyl groups) were synthesized and characterized using powder XRD and Transmission Electron Microscopy (TEM) Then, we investigated the surface structure of blended poly-3-hexylthiophene (P3HT) and CdSe active layer using Atomic Force Microscopy (AFM). Subsequently, absorption spectroscopy (UV–Vis) and photoluminescence (PL) were used for further optical property characterization. Significant quenching of PL spectra along with a larger absorption band were observed. Importantly, the capping ligand effect on the morphology and the fluorescence quenching was investigated in order to high light the role of ligand modification on the photovoltaic device performance. We reported a performance dependence of hybrid devices on the bulkiness of capping molecules. Moreover, the conversion efficiencies of the elaborated cells show an increase from 0.046% for pure P3HT to 0.46% for the hybrid composite containing Pyrr3PO-capped NCs.