| Abstract |
To shed light on some very crucial aspects regarding InGaN as a material system and explore its potential for novel photovoltaic applications, we will initially present a detailed study on the fundamental optical properties of InGaN alloys in the entire compositional range grown by MBE, since some of them were unknown up to now. The necessity for accurate knowledge of the composition dependent optical properties, such as the emission energy, the refractive index and the band gap, is of particular importance for the proper device design and realization not only for solar cells but also for any InGaN-based optoelectronic device. Next, we deal with another very important aspect regarding the efficient performance of InGaN-based optoelectronic devices which is oriented from the alloy compositional inhomogeneities, namely carrier localization. High In content alloys were studied for this purpose, and it was found that localization can be efficiently tuned by the proper selection of substrate temperature and growth environment. The correlation between growth kinetics and optical properties could paved the way to the on-demand growth of InGaN-based optoelectronic devices depending on application requirements.
Until now, most of the research development on InGaN solar cells is based on the fundamental double-heterojunction design of III-nitride LEDs. In such configurations, the direction of polarization-induced electric field is against the built-in electric field of the junction due to the presence of polarization charges and, consequently, the efficient collection of photo-generated carriers is impeded. Here, the non-conventional p-side down design is theoretically studied in depth to explore its potential for high-efficiency InGaN-based photovoltaic devices. Also, a realistic device is proposed reaching conversion efficiency up to 14.5%, under AM 1.5G illumination, revealing the potential of InGaN single junction solar cells.
The potential of InGaN alloys for low cost large area photovoltaic applications has been also investigated. Polycrystalline InxGa1-xN alloys were deposited on fused silica glass and their structural, optical and electrical properties upon increasing annealing temperature were studied in depth. Then, following the cost-effective large area scheme, the photovoltaic operation of two distinct InGaN/Si modules have been theoretically investigated, using realistic material parameters. It was found that the efficiency of a standard np-Si solar cell can be enhanced by ~30% by using a properly designed n-InGaN window layer. The conversion power efficiency from 15.05% can be boosted up to 19.55% employing the proposed n-InGaN/np-Si structure. Also, by adapting the optimized current-matched pn-InGaN/pn-Si tandem module, efficiency can be as high as 27.52%, highlighting that InGaN alloys have the potential to be strong competitors in the area of cost-effective solar cells.
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Optoelectronic characterization and modeling of InGaN heterostructures for photovoltaic applications
