Power conversion efficiency enhancement in natural-dye-based DSSC
a Laboratorio de Biomateriales, Instituto de Química Biológica, Facultad de Ciencias, Universidad de la República. Igua 4225, 11400 Montevideo, Uruguay.
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
London, United Kingdom, 2023 June 12th - 14th
Organizers: Tracey Clarke, James Durrant and Trystan Watson
Publication date: 30th March 2023

Dye-sensitized solar cells (DSSC), or Grätzel cells, consist of three major components: semiconductor, sensitizer and electrolyte (placed between two electrodes). A liquid redox electrolyte typically consists of a redox mediator, additives and a solvent. The photovoltaic performance of DSSC depends on the electrolyte and the solvent used to build it. The redox couple is responsible for dye regeneration and charge transport between the two electrodes. In addition to a redox couple, various additives as specific cations or compounds are typically introduced into the liquid electrolytes to enhance the photovoltaic parameters of the operating cells. These electrolyte additives are expected to be adsorbed onto the TiO2 surface, thus affecting the CB in the TiO2 strongly associated with the photocurrent and photovoltage.

In this work, photoanodes were sensitized with different dyes (carotenoids and anthocyanins) obtained from natural resources. DSSCs were assembled using two different electrolytes: one with and the other without additives. The photovoltaic parameters were then compared for DSSC built up using two electrolytes: a- Iodolyte AN-50 50 mM acetonitrile with pyridine derivative (AN50) and b- LiI 0.8 M + I2 0.05 M acetonitrile valeronitrile 85/15 (AV8515).

DSSCs were built as open cells and then characterized using electrochemical techniques under an incident light power of 1 sun from a solar simulator. The J vs E profiles and the electrochemical impedance (EIS) records were obtained under light incidence and darkness.

Main electrochemical parameters (as PCE= power conversion efficiency and FF= fill factor) were obtained from the J vs E profiles using the two electrolytes. DSSCs were assembled using different natural sensitizers named: E5, a cyanobacterial’s extract (mainly containing zeaxanthin, myxoxanthophyll and chlorophylls); DEL3GLU, a blueberries extract (mainly composed of delphinidin-3-glucoside); and CYA3GLU, extracted from Erythrina crista-galli flowers (mainly cyanidin-3-glucoside). Results arise from at least three independent experiments.

PCE increased 1.5 to 2.5 times in the presence of AV8515 (instead of AN50). Results were mainly raised when anthocyanins were the sensitizers under evaluation. But FF values showed the opposite. FF values ranged between 0.55 to 0.70 for DSSCs containing AN50, whereas for those containing AV8515, FF values are inside the 0.44 to 0.49 values.

The records showed that power conversion efficiency for DSSCs assembled using AV8515 is increased compared with PCE for cells containing AN50. On the opposite, the fill factor FF is higher for cells with AN50. Voc (open circuit voltage) is also lower for DSSC using the AV8515 electrolyte (within the 0.3 to 0.4 V range), whereas for DSSC containing AN50, the Voc values lie in the 0.5 to 0.6 V range. But Jsc (the short-circuit current density) is lower for AN50-containing cells.

EIS measurements recorded at 0.4 V align with those observed at the J vs E profiles: total impedance values (composed of several resistance and capacitance elements) are higher when lower PCE values are recorded. Then, in the Nyquist representation of the measured impedance, lower semicircles are observed for cells containing AV8515. 

Summarizing: for natural dyes, using AV8515 as the electrolyte, that is, without pyridine additives, allows to build more efficient DSSCs, but affects some parameters such as Voc and FF, as well the cells' stability along the time.

I thank Dr Sylvia Bonilla and Tatiana Montagni for providing the analyzed dyes. I am also a PEDECIBA and ANII researcher.

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