Researchers have doped silicon dioxide gel with an embedded rare-earth element to produce a luminescent modified silica gel1. The gel has antireflective properties that could enhance the efficiency of solar cells. It also absorbs both visible and ultraviolet light, making it usable in solar cells either on Earth as well as in space.
Silica gel is an excellent host material for rare-earth ions. The researchers doped silica sol with the rare-earth element europium and then converted it to silica gel under controlled temperature. The doped silica gel was allowed to age for a week to form silica xerogel, a solid form of silica gel.
Sophisticated imaging techniques showed a large number of nanosized black spots (or pores) within the silica matrix. The researchers believe the europium ions may be trapped within these pores. The gel surface contained pores in the size range of 10–15 nm and particles in the size range of 100–150 nm.
The silica gel showed broad absorption between the ultraviolet and visible light regions. This can be used to increase solar cell performance by converting the otherwise wasted UV or blue light into red light, which can then be readily absorbed by the solar cell.
In a conventional photovoltaic device, nearly 35% of the incoming light is reflected by the front surface. The modified silica gel layer exhibited a reflectivity of less than 4%.
Silica gel layer could therefore be used as an antireflective coating. "A solar cell antireflection layer is essential for minimizing the loss of incident solar radiation by reflections from the surface," says lead researcher Santa Chawla. The silica gel layer could be a prospective future material for improving the performance of silicon solar cell, she adds.
The authors of this work are from: National Physical Laboratory, Council of Scientific and Industrial Research, and Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi, India.
