(Invited) Amphiphilic Block Copolymers and Their Hybrids for Efficient Aqueous-Processed Solar Cells

Abstract

Due to their low cost and high efficiency, polymer/nanocrystal hybrid solar cells have attracted much attention in recent years. Additionally, aqueous-processed solar cells are attractive because they exhibit the potential to produce clean energy via the use of nontoxic solvents. The use of water instead of toxic organic solvents during the fabrication process of these devices is capable of significantly reducing the environmental impact as well as the production cost. In aqueous-processed solar cells, hybrid solar cells employing water-soluble conjugated polymers and inorganic nanocrystals as photovoltaic materials have gained much attention. These hybrid materials take advantage of both water-soluble conjugated polymers and nanocrystals, which exhibit adjustable absorption properties through structural modification, efficient charge carrier generation, and high charge carrier mobility. Water-soluble conjugated polymers are typically homopolymers with ionic (i.e., sulfonate and phosphonate moieties) or nonionic, hydrophilic (i.e., hydroxyl and glycol moieties) side chains. Unfortunately, the use of hydrophilic side chains in these conventional water-soluble conjugated polymers adversely affected the stacking of the polymer backbone, which can lead to the deterioration of their optoelectronic properties and thus a lower power conversion efficiency in solar cells. Furthermore, these side chains may cause charge trapping when applied in the active layer, which results in the further reduction in performance In this presentation, the use of a water-soluble hybrid material consisting of amphiphilic block copolymers and cadmium telluride nanocrystals as the active layer in hybrid solar cells will be discussed. The amphiphilic block copolymers composed of poly(3-hexylthiophene) (P3HT) and poly(acrylic acid) (PAA) self-assembled into ordered nanostructured micelles which then transformed to nanowires by co-micellization with P3HT additives. Furthermore, after annealing, the hybrid materials formed an interpenetrating network. The properties of the hybrid materials and the film morphology, and how they correlate to the device performance will be discussed.