Synthesis of new nanocrystal-polymer nanocomposite as the electron acceptor in polymer bulk heterojunction solar cells

A hydroxyl-coated CdSe nanocrystal (CdSe-OH) and a CdSe-polymer nanocomposite were synthesized and used as the electron acceptors in polymer solar cells (PSCs). The CdSe-polymer composite was prepared via atom transfer radical polymerization (ATRP) of N-vinylcarbazole on functionalized CdSe quantum dots. Physical properties and photovoltaic characteristics of the CdSe-poly(N-vinylcarbazole) (CdSe-PVK) nanocomposite have been investigated. Thermogravimetric analysis (TGA) results displayed higher thermal stability for CdSe-PVK nanohybrid in comparison with the linear-type PVK polymer. Differential scanning calorimetry (DSC) studies indicated that CdSe-PVK had a lower glass-transition temperature (Tg) in comparison with PVK due to the branch effect of the star-shaped polymer hybrid. Cyclic voltammetric (CV) measurements were performed to obtain HOMO and LUMO values of PVK and CdSe-PVK. TEM and SEM micrographs exhibited CdSe nanoparticles were well coated with PVK polymer. Both CdSe-OH and CdSe-PVK were blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction solar cells. Polymer solar cell based on CdSe-PVK as acceptor revealed that the photovoltaic properties can be significantly improved when PVK polymer chains were grafted on surfaces of CdSe nanocrystals. In comparison with the P3HT:CdSe-OH system, PSC based on P3HT:CdSe-PVK showed an improved power conversion efficiency (0.02% vs. 0.001%). Film topography studied by AFM further confirmed the better device performance was due to the enhanced compatibility between P3HT and CdSe-PVK.