|Nofrijon Sofyan||Department of Metallurgical and Materials Engineering, Faculty of Engineering Universitas Indonesia, Indonesia|
|Aga Ridhova||Universitas Indonesia|
|Akhmad Herman Yuwono||Universitas Indonesia|
|Arief Udhiarto||Universitas Indonesia|
Platinum is the most effective counter electrode for use in dye-sensitized solar cells (DSSC). However, as platinum is very expensive, its price impedes its broad use as a DSSC counter electrode. As an alternative, carbon has been used for this purpose. In this study, carbon has been successfully pyrolyzed from the precursors of table sugar and sucrose through a chemical process, i.e. the dehydration of the precursors with sulfate acid followed by a pyrolysis process, and used as Pt-less counter electrode in a DSSC device. The as-synthesized carbon was characterized using X-ray diffraction (XRD) to obtain crystal structure information and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) was employed to carry out morphological and compositional examination. The material activity and performance of the counter electrode in the DSSC device were analyzed using a semiconductor parameter analyzer through current–voltage characteristic curves (I-V). The results show that the precursors of table sugar without the addition of a metal catalyst and with initial heat treatment at 300°C for 1 hour, and of sucrose with a catalyst could produce carbon with a particle size of around 600–900 nm. The I-V curve characteristic of the DSSC device assembled using carbon produced from sucrose as a counter electrode resulted in a power conversion efficiency (PCE) of only 0.041%, whereas the DSSC device assembled using carbon produced from table sugar as a counter electrode exhibited a good performance with a PCE of 3.239%, almost equivalent to that of platinum paste with a PCE of 4.024%. This result is promising in terms of using a cheap source of carbon for the Pt-less counter electrode.
Dye-sensitized solar cell; Power conversion efficiency; Pt-less counter electrode; Sucrose; Table sugar
In the midst of today’s ever-increasing energy demands, the oil and gas sector can no longer be expected to serve as a primary source in supplying these demands. The main reason for this, in addition to its decreasing availability, is that the resulting emissions of these fossil-based fuels are not environmentally friendly. Hence, an alternative energy source is required to overcome this problem and to compensate for the shortage of oil and gas resources. One of the possible alternatives, especially for tropical countries constantly exposed to sunlight, is to harness the abundant energy resource provided by sunlight through the use of solar cell devices. One type of solar cells that may be used are dye-sensitized solar cells (DSSC).
A DSSC is a third-generation solar cell first introduced by O'Regan and Grätzel (1991). The working principle of this DSSC is based on the photo-electrochemical principle in which the electrons of the dye will be excited after being exposed to light such that the dye will be in an oxidized state. The electrons will be injected into a semiconductor conduction band that acts as a photoanode. The electron charge on this photoanode is transferred to the opposite electrode, which is known as the counter electrode. This counter electrode will collect electrons and catalyze the reduction of electrolyte, which is usually in the forms of triiodide into iodide, enabling the reaction result to regenerate the lost electrons from the dye (Chen & Shao, 2016). In this instance, the counter electrode is one of the components that has an important role in the performance of the DSSC.
In order for a material to be used as a counter electrode, it must have high conductivity, good electro-catalytic properties, and good chemical stability (Wang et al., 2014). Due to its inherent properties, platinum (Pt) would be the best option for a DSSC counter electrode. However, the high price of platinum impedes its broad use in DSSC devices. For this reason, various other materials have been studied with the aim of producing a Pt-less counter electrode. Among these substitute materials are a conductive polymer with a power conversion efficiency (PCE) value of 7.15% (Li et al., 2008b), a composite material with a PCE value of 5.69% (Al-Bahrani et al., 2015), and a metal oxide with a PCE value of 8.48% (Du et al., 2017).
Carbon and its allotropic variety has also been extensively investigated as a cheap platinum-less counter electrode. This is because carbon material, in addition to involving relatively cheaper production costs and being more abundant, also meets the three requirements of the DSSC counter electrode, i.e. high conductivity, good electro-catalytic properties, and good chemical stability (Wang et al., 2014). Among the various carbon allotropes, carbon black has the most accessible structure, and the cost of its fabrication is also relatively lower than that of other structural fabrications. Research has found that a carbon black counter electrode could achieve a PCE of 8.29%, close to the value produced by a DSSC with a platinum counter electrode: a PCE of 8.35% (Wu et al., 2016). The use of carbon black, however, should be avoided due to its possible carcinogenic effect on humans (Ramanakumar et al., 2008).
this study, DSSC devices have been successfully fabricated using carbon
pyrolyzed from the low-cost resources of table sugar and sucrose as counter
electrodes. The results show that carbon with particles close to nanosize could
be obtained using table sugar as a precursor by preheating to 300°C for 1 hour without the addition of a catalyst (600?630
nm), and using sucrose with the addition of a catalyst (900 nm). The DSSC
device fabricated from the carbon produced using table sugar as a counter electrode
exhibited a PCE of 3.239%, whereas the carbon resulting from the use of sucrose
as a counter electrode demonstrated a PCE of only 0.04%.
authors would like to express their gratitude for the funding from the
Directorate of Research and Community Services (DRPM), Universitas Indonesia,
through Hibah PITTA No. 823/UN2.R3.1/HKP. 05.00/2017.
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