(Brookhaven National Laboratory)
Scientists have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters). This is the first such material blending semiconductors and fullerenes to be formed to absorb light and efficiently generate charge and charge separation. The material remains largely transparent because the polymer chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers.
The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporated, the polymer formed a hexagonal honeycomb pattern over a large area
Credit: BNL and Chemistry of Materials
The scientists verified the uniformity of the honeycomb structure with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy. The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.
In terms of practical applications, the material could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.
Structural dynamics and charge transfer via complexation with fullerene in large area conjugated polymer honeycomb thin films
Chemistry of Materials, Article ASAP DOI: 10.1021/cm102160m
Publication Date (Web): November 1, 2010
Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)