Influence of concentration of anthocyanins on electron transport in dye sensitized solar cells

Abstract

The influence of concentration of anthocyanins in dye sensitized solar cells (DSSC) has been investigated, with focus on how concentration influence electron transport. The influence on electron transport was then linked to solar cell performance. Anthocyanins were extracted from fresh flowers of Acanthus pubscenes using methanol acidified with 0.5% trifluoracetic acid, concentrated using a rotary evaporator and partitioned against ethyl acetate. Concentration of the anthocyanins was determined using Keracyanin Chloride as a standard. DSSC were fabricated using Titanium dioxide as anode, anthocyanins as sensitizers and Platinum as counter electrode material. Titanium dioxide was deposited on Fluorine doped Tin oxide glass substrate using slot coating method. Platinum was deposited on FTO glass substrate using a brush previously dipped in plastisol precursor, and annealed at 0 C for 20 min to activate Platinum. Dye sensitized solar cells were assembled using anthocyanins at varying concentrations. Performance parameters of the solar cells were measured using a solar simulator which was fitted with digital source meter. Electron transport parameters were studied using electrochemical impedance spectroscopy (EIS). Open circuit voltage, short circuit current and fill factor were observed to increase with concentration of anthocyanins. The increase in solar cell performance was attributed to increase in charge density which led more charges being available for transported to solar cell contacts. The increased charge resulted in a negative shift in Fermi level of electrons in the conduction band of TiO 2 . The shift in Fermi level resulted into an increase in open circuit voltage and the overall solar cell performance. EIS studies revealed increase in recombination resistance with concentration of anthocyanins. The increase in recombination resistance was found to be related to increase in electron density, and hence the shift in the Fermi level of electrons in the conduction band of TiO 2 .

Influence of the pH of anthocyanins on the efficiency of dye sensitized solar cells

“…In contrast to the absorption properties of anthocyanins at varying concentrations, we reported a consistent increase in absorbance as the concentration increased, in accordance with the Lambert–Beer law [ 9 ]. This is different from the absorbance properties of Figure 2 that have been described in the preceding paragraphs.…”

“…Cleaning of FTO glass substrates, deposition of platinum and preparation of titanium paste were performed following the procedure in our previous work [ 9 ]. Briefly, FTO glass substrates were first cleaned using a 1% solution of Helmanex III in an ultrasonic bath for 20 min and rinsed three times with deionized water.…”

“…The electrode materials are usually deposited on conducting glass substrates such as fluorine-doped tin oxide (FTO) or indium tin oxide (ITO) [ 3 ]. The glass substrates in addition to supporting the electrode materials also provide cell contacts [ 9 ].…”

“…At the same time, the electrolyte donates an electron to the dye, compensating for the electron that was injected into the conduction band. The electrolyte then receives another electron from the counter electrode, a process that is catalysed by platinum [ 9 , 11 ].…”

“…While previous studies [ 15 , 16 ] explored the performance of anthocyanins in dye-sensitized solar cells, they did not explain the performance in terms of electron density in relation to different molecular forms exhibited by anthocyanins in different pH environments. Additionally, in our previous study, we investigated the influence of the concentration of anthocyanins on electron transport in dye-sensitized solar cells at a constant pH of the sensitizing anthocyanins [ 9 ]. Improvement in photovoltaic performance as the concentration of anthocyanins increases was observed.…”