What is DSSC?

A classical dye sensitized solar cell (DSSC), also known as Grätzel cell, is a photoelectrical conversion device which has a sandwich structure consisting of a dye-sensitized TiO2 photo-anode, a platinized conducting glass (Pt-FTO) counter electrode (CE) and an I-/I3- electrolyte. The structure of DSSC is shown in Figure 1. The photo-anode and counter electrode are placed on either side of the electrolyte. In the DSSC, a dye is used to absorb incoming sunlight to produce excited electron that injects into conduction band (CB) of TiO2 layer, and then the oxidized dye is reduced by I- in electrolyte. The injected electrons flow though CB of TiO2 and FTO towards the transparent electrode via external circuit to reach the CE. The I3- gets a electron from CE to be reduced. The whole process is a pure energy conversion without mass loss.

Figure 1

Figure 1

During the past more than two decades, DSSCs have been intensively investigated and developed. Expect the typical Ru-based dye, organic dyes and porphyrin dyes have also been used in DSSCs and achieved promising efficiencies. Organic compounds and metal complexes (Co, Cu, Mn, Fe, etc) have been adopted as redox couples instead of the I-/I3- one. For CE, economic polymer (PEDOT, PANI, etc) and metal sulfide/oxide have been utilized to replace the expensive Pt-FTO. After trying different combinations and attempts, currently, the world record efficiency of 14% in a liquid DSSC is obtained with an alkoxysilyl-anchor dye of ADEKA-1 AND A Carboxy-anchor dye lEG4 as co-sensitizer, Co(II/III)(phen)3 as redox couple and GNP(graphene nanoplatelets) CE (ref ). In order to replace the liquid phase in the classic DSSCs, the solid state DSSCs is proposed and reported in 1998 by Grätzel at EPFL(ref). Solid state hole transport materials (HTMs) are employed instead of liquid redox couple undertaking electron transport between CE and photo-anode. The highest efficiency of solid state DSSCs is reported as 7%. P-type DSSCs is using a p-type semiconductor, such as NiO, insteat of n-type semiconductor and perform an invert electron transfer process in comparison with classic DSSCs.

 The DSSC has a number of attractive features. It is simple to make using conventional roll-printing techniques. DSSC offers the possibilities to design solar cell with a large flexibility in shape, color and transparency. DSSC performs also relatively better compared with other solar cell technologies under diffuse light conditions and at higher temperatures. And most of the materials used in DSSC are low-cost. On the basis of DSSC research, some concepts also have been used in other photovoltaic devices, such as in Perovskite solar cells and organic solar cells, to form the hybrid solar cells.

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