Estudo de eletrólito polimérico de base natural para aplicação em células solares do tipo CSSC e QDSSC

Abstract

Sensitized solar cells, among the so-called emerging cells, enable the use of low cost materials. Natural dyes and polymers are examples of such materials with promising prospects for solar cell applications. This work aims to study natural polymers for use in solar cells sensitized by CdS and CdSe/CdS quantum dots and proposes co sensitization, combining a natural dye extracted from the Amazonian jenipapo fruit and CdS. A study was conducted to find the best composition for preparing polymeric electrolytes, using cassava gum, xanthan gum, and corn starch, with better results obtained using glycerin as a plasticizing agent and formaldehyde as a cross-linking agent. Cassava gum performed better in preliminary photoelectrochemical characterizations in CdS sensitized devices and was selected for further study. Several attempts were made to dope the polymeric electrolyte with citric acid, acetic acid, and lithium perchlorate. The latter showed better compatibility, and its concentration was optimized through electrochemical impedance spectroscopy studies at diFFerent temperatures to obtain the conductivity of prepared films. The dielectric property and electrical conductivity of the polymeric electrolytes were studied in the frequency range of 2 MHz to 20 mHz. The optimal doping concentration was 2%, achieving an electrical conductivity of 1.48 x 10-2 S.cm-1 . When employing the polymeric electrolyte in CdSe/CdS sensitized cells, an eFFiciency of 5.51% was measured, higher than the liquid electrolyte, which was 4.97%. The stability of the cells was monitored by analyzing their photoelectrochemical parameters for seven days, during which the eFFiciency of the device containing the polymer electrolyte decreased by 22.63%, and the liquid electrolyte by 52.9%. Regarding the study of natural dye, results from UV-vis absorption analyses and photoelectrochemical characterizations ensured the potential for co-sensitization by natural pigment and quantum dot photoanodes. These photoanodes were tested in cells using S2- /Sn 2- or I- /I3 - as redox electrolytes. Although the results of co-sensitized cells were inferior to cells sensitized only with CdS or N3, co-sensitized solar cells using the natural jenipapo dye showed better photovoltaic conversion eFFiciency (jenipapo dye/CdS = 0.70%) and stability compared to cells co sensitized with the conventionally used synthetic dye N3 (N3/CdS = 0.25%). Additionally, new counter electrodes using graphene with cobalt and nickel metals were studied. The simultaneous electrodeposition of graphene and metals indicated that cobalt exhibits a better kinetic response for electron transfer when a polysulfide electrolyte is used. This work demonstrates the potential of natural polymers and dyes from the Amazon region for applications in new solar cell technologies.