Transparent light-harvesting materials

Article By:

Cotlet, Mircea Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York.

Xu, Zhihua Brookhaven National Laboratory, Upton, New York.

Wang, Hsing-Lin Los Alamos National Laboratory, Los Alamos, New Mexico.

Tsai, Hsinhan Los Alamos National Laboratory, Los Alamos, New Mexico.

Last reviewed:2012

DOI:https://doi.org/10.1036/1097-8542.YB120380

Solar cells, or photovoltaics (PVs), have been developed as a promising technology for renewable energy. Among solar cells, organic photovoltaic solar cells (OPVCs), or the technology to convert sunlight into electricity using thin films of organic semiconductors, such as conjugated polymers, have been under intense research over the past decades as potential cost-effective replacements for the more expensive but currently more efficient silicon-based devices. OPVCs provide several attractive features, including the use of cheap, lightweight plastic materials (conjugated polymers) with good solubility in common organic solvents, cost-effective processing methods (such as printing and dip- and spin-casting techniques), and mechanical flexibility. In polymer-based OPVCs, the conjugated polymer, usually an electron donating (p-type) semiconducting material, harvests the light to create an excited state known as exciton (an electron and a hole bound together). Excitons can be separated into electrical charges by using appropriate electrical fields, for example by the use of electrodes with different work functions, such as indium tin oxide (ITO) [with high work function] and aluminum (Al) or gold (Au) [low work function]. There are several known OPVC device architectures, including single-layer (conjugated polymer) OPVCs, double-layer OPVCs (electron donor-acceptor layers using polymer plus dye, p-type plus n-type conjugated polymers, or polymer plus fullerene combinations), multilayer PVs (alternations of donor and acceptor materials), or bulk heterojunction PVs (blended polymer-fullerene composites). The addition of electron-accepting materials [dyes, fullerenes (C₆₀ and its derivatives) or n-type conjugated polymers] enhances exciton dissociation into separated charges, thus improving the power conversion efficiency of OPVCs. Bulk heterojunction OPVCs based on blends of conjugated polymers and fullerenes are technologically the most promising, with current reports claiming power conversion efficiencies as high as 8%.

The content above is only an excerpt.