Filtro óptico de radiação para células solares utilizando filmes finos multicamadas de óxido de índio e estanho e prata

Abstract

The increase in global energy demand has led to massive consumption of fossil fuels, intensifying climate change. Electricity accounts for one-third of this demand – more than half concentrated in buildings, with 50% of this consumption for thermal comfort systems. To supply electricity generation in a clean and sustainable way, several alternative and renewable sources have emerged, with solar energy standing out as the most promising on a large scale. However, this technology still faces some challenges and is close to the point of maximum efficiency of the main material that makes up these photovoltaic conversion devices, silicon. However, other materials are emerging and new photovoltaic cells are being developed. Furthermore, current solar cell materials are not capable of absorbing the complete solar electromagnetic spectrum for energy generation, with a large portion of the energy being absorbed as heat – generating warming, loss of efficiency, and degradation. Therefore, this work proposes optical radiation filters with the aim of transmitting to photovoltaic cells only the radiation range suitable for the photoelectric effect and reflecting the undesirable radiation range. The optical filter is a thin multilayer film composed of alternating indium tin oxide (ITO) and silver (Ag), where the optical properties were simulated and optimized via software (OpenFilters) with respect to the number of layers (3 and 5) and thicknesses. The films with the best performance were manufactured by magnetron sputtering and annealed at 350 °C for 1 hour in a muffle furnace. Optical characterizations were performed by UV-Vis spectrophotometry and heat blocking tests with a thermographic camera in an outdoor environment after exposure to solar radiation for 1 hour. Simulations demonstrate that the film with the best results for the desired regions of the solar spectrum is ITO/Ag/ITO/Ag/ITO (IAIAI) with 35/5/80/5/35 nm (T = 83.65% in the visible spectrum and R = 87.29% from 1100 to 2500 nm). However, it was not possible to manufacture it satisfactorily, resulting in poor transmittance and thermal blocking results. The IAIAI10 film showed good simulation results (T = 66.41% in the visible spectrum and R = 93.50% from 1100 to 2500 nm) and spectrophotometry results (T = 66.17% in the visible spectrum and T = 5.65% from 1100 to 2500 nm), as well as satisfactory thermal blocking (an increase of 4 °C after 1 hour, versus increases of 8 to 22 °C in other samples). In both films, the heat treatment was not satisfactory. Thus, this work produced optical radiation filters that show potential for use in solar cells to reduce the operating temperature and, consequently, mitigate efficiency losses due to heating during the energy generation process.