The Texas researchers used a 12-period multi-quantum well (MQW) structure consisting of InGaN/GaN (3nm/16nm) with the In content of the well targeted at 35% (Figure 1 above). The layers were deposited by metal-organic chemical vapor deposition (MOCVD) on sapphire. The wavelength of the electroluminescence from the structure was around 533nm (green).

The researchers comment that “obtaining InGaN/GaN MQW structures with a total InGaN light-absorption layer thickness of around 200nm is another challenging task.”

“However, the results indicate the strong potential of InGaN-based MQW solar cells for concentrated photovoltaic (CPV) applications,” the researchers say and they believe that the efficiency under concentrated sunlight could be further enhanced by improving interfacial quality between InGaN and GaN by reducing dislocation density at the interface through further growth and device processing optimisation.

Glass optimisation also underway

The Construction Unit at Tecnalia Spain (right) in conjunction with the University of Cantabria has taken part in the Sunglass project, aimed at developing a new building product or a glass that augments the efficiency of photovoltaic (PV) solar systems, to boost having more renewable energy in the construction sector.

The challenge for the Sunglass project is to boost the use of PV solar energy by increasing performance of currently existing solar panels (currently with a performance around 15 %.)

Research to date has focused on modifying the semiconductor material to make use of a greater part of the solar spectrum. The Sunglass project puts forward an alternative approach, involving the "conversion of frequencies" phenomenon — based on absorbing photons of certain frequencies and emitting another range of frequencies.

Study in photoactive compounds
Various photoactive compounds were investigated for the project with the aim of determining their capacity to absorb high-frequency radiation in order to subsequently emit it at ranges more effective for solar cells, as well as the possibility of implementing such materials in the glass coating of solar panels.

These compounds were used to develop special glass for these photovoltaic applications and substituting the current glass of solar panels by the new product, obtained increased energy efficiency.

By means of the "conversion of frequencies" produced by the glass, the radiation incident on solar cells is more effective and gives rise to a 2-3% increase in their efficiency. This boost in the production of clean energy without acoustic contamination, avoids greenhouse gas emissions, and complements other energy sources.