Photovoltaic Efficiency Improvement Employing Photoluminescent Nanostructures
Silicon based solar cells have captured the largest portion of the total market of photovoltaic devices, mostly due to its relatively high efficiency at relatively affordable prices. Also, in recent years, photovoltaic devices have been researched with the aim of improving their power conversion efficiency employing different methods including surface nanotexturization, antireflection coatings, surface passivation schemes, among others. However, silicon as any other material, exhibits some limitations in the energy conversion due to its absorption range of light. The underlying reason is that in principle only photons with energy greater than the bandgap can be absorbed, leading to the loss of relatively low energy photons. But even photons with energies larger than the bandgap have a non-negligible probability of interacting with vibrational modes or crystal phonons, in a process referred to as thermalization, rather than producing electron-hole pairs.
These fundamental losses can be ameliorated by the utilization of luminescent materials. To promote the absorption of low energy photons (near and below the bandgap), particles with up-conversion properties can be employed. This effect can be succinctly described as the absorption of low energy photons and the emission of higher energy photons that are able promote the formation of electron-hole pairs in the substrate employed. On the other hand, in the case of energetic photons that contribute to thermalization, the alternative is to employ down-shifting materials, which are able to absorb high energy photons and emit lower energy photons that fall within the range of absorption by the underlying solar cell. In this work, semiconductor quantum dots and semitransparent Chlorophyll-A/PMMA films were produced for application in photovoltaic technologies as photon downshifting layers on functional solar cells. Other approaches have used quantum dots in photovoltaic (PV) techniques as active layers involving electron or hole transport process, however, in most cases the materials and/or methods employed could pose a challenge during manufacturing because of production costs and/or the processing times involved. In contrast, in this study, we present cost-effective quantum dot synthesis process employing well known materials including Silicon, CdSe and CdS as well as a relatively straightforward chlorophyll extraction method. The proposed methods represent a promising and cost effective alternative to achieve higher efficiencies in photovoltaic devices. The studies performed on the deployment of the nanostructures described herein have demonstrated increases up to approximately 12% in the power conversion efficiency of the photovoltaic devices. These results demonstrate that the application of down-converting materials is a viable strategy to improve the efficiency of Silicon solar cells with mass-compatible techniques that could serve to promote their widespread utilization.