Theoretical and experimental study of solar cells based on nanostructured films of TiO2 sensitized with natural dyes extracted from Zea mays and Bixa orellana.

Abstract

Natural dyes were extracted from Zea mays and Bixa orellana, products from Peru, for the sensitization of nanoporous titanium dioxide (TiO2) films. The manufactured DSSCs were studied from the theoretical and experimental point of view in two main stages. In the first, the computational simulation of the dye molecules was carried out using the DFT and TD-DFT method. The analysis was complemented with UV-visible characterization. In the second stage, the transport and recombination processes that occur in the solar cell were studied. For this, the methods of small-modulation transient measurements, extraction of charges and impedance spectroscopy were used. Computational simulations determined that cyanidin-3-glucoside (C3G), the main component of Zea mays, sensitizes the TiO2 film by means of a monodentate anchor through one of the hydroxyl groups. For its part, bixin, which makes up Bixa orellana, anchors through the carboxyl group and also showed a tendency to form agglomerates on TiO2. The charge extraction technique allowed establishing the distribution of trap states of the sensitized films. Small-modulation transient measurements provided information on time constants and diffusion coefficient. It was concluded that the film sensitized with C3G presented a higher density of trap states and a lower level in the conduction band, which resulted in shorter electron life times. The bixin-sensitized film presented better diffusion for its free charge carriers. This was corroborated with impedance spectroscopy, in which the diffusion length parameters pointed to the bixin cell with better charge collection efficiency. All the results were in agreement with the characteristic curves of current–voltage and with the spectral curve of efficiency of conversion of incident photons to electrons (IPCE).