Finding a substrate material for solar cells that simultaneously provides a high optical transparency and a high transmission haze is challenging. It now appears that an engineered paper could be an ideal substrate. Scientists have developed a wood-fibre-based nanostructured paper that provides a transparency of ~96% and a haze of ~60%. This material is potentially useful for photo-voltaics, where it could reduce the angular dependence of light harvesting for solar cells, and it could also benefit outdoor displays by reducing glare and specular reflections of sunlight. (Initial demonstration can be seen in Nano Lett. 14, 765–773; 2014).
The team produced the transparent paper by using an oxidation process called TEMPO to introduce carboxyl groups into the cellulose fibres of wood. This process weakens the hydrogen bonds between the cellulose fibrils, causing the wood fibres to swell. The result is a paper with a much higher packing density than usual and greatly improved optical transparency and haze.
Analysis by scanning electron microscopy revealed that the transparent paper has a homogenous surface as a result of voids being filled by small fibre fragments. In the spectral range of 400–1,100 nm, the transparent paper had a transmittance of ~96% and a transmission haze of ~60%.
The benefits of the enhanced haze of the transparent paper for photo-voltaic devices were demonstrated by laminating the paper to the top of an organic solar cell and measuring the cell’s photo-current as a function of the incident angle of white light.
According to the authors, the improvements can be explained by two factors i.e. the reduced reflection of the light due to the low index contrast between the top layer of the photo-voltaic device and the transparent paper, and the directional change of the incident light in the transparent paper.
Scientists are pushing for further results regarding efficiency of Solar Cells by modifying them with paper developed using this technology. With promising initial results, can this technology will be helpful in decreasing the efficiency bottleneck of the Solar Cells – we have to wait.
Edited and Extracted from article by Noriaki Horiuchi in Nature (doi:10.1038/nphoton.2014.43)