DSSC devices

The first seminal woik on DSSC was reported in 1991 by O Regan and Gratzel [O RE 91]. The originality and the device performances ofDSSC are mainly governed by (i) the high surface area and the controlled nanoporosity of the oxide materials and (ii) the high efficiency regeneration of the photo-oxidized dye molecules induced with a redox mediator in electrolyte. 

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Fig. 33 Power conversion efficiency and fill factor of varying amounts of graphene concentration on DSSC devices. (Reprinted with permission from [270])...

Park et al. [18] reported the synthesis of dye-sensitized solar cells (DSSCs) based on electrospun polymer blend nanofibers as electrolytes. Electrospun poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) and PVDF-HFP/polystyrene (PS) blend nanofibers were prepared as shown in Figure 1.16. The authors reported that the photovoltaic performance of dye-sensitive solar cell (DSSC) devices using electrospun PVDF-HFP/PS (3 1) nanofiber was much better as compared to DSSC devices using electrospun PVDF-HFP nanofiber. It was further observed that the overall power conversion efficiency of the DSSC device using PVDF-HFP nanofiber had a lower value than that of the DSSC device using electrospun PVDF-HFP/PS blend nanofibers... 

The photoelectrochemical solar cells form the first family of organic photovoltaic devices. Typically, the active layer of such devices consists of nanostructured and dye sensitized electrodes, whereas the other electrode (counter electrode) is separated by an electrolyte or hole conductor. The highest efficiency of around 11% is achieved in dye sensitized solar cells (DSSCs) using TiO nanostructured electrodes. Schematic layout of a typical DSSC device is shown in Figure 2 ... 

Figure 2 Schematic layout of a typical DSSC device. (Reproduced from Ref. 36. American Chemical Society, 2009.)...

For instance, organic or organometallic dyes in the case of DSSC devices serve as an electron donor material. However, such dye has no role in hole transport and therefore... 

Figure 9 (a) Schematic layout of a DSSC device based on a transparent titanium dioxide nanotube array covered with organic dye... 

The characterisation of a DSSC device or the study of partial processes that occurs at such cells uses a series of optical and electrochemical techniques, either stationary or time-resolved. The studies cover a wide range of timescales, accompanying the wide time span of phenomena occurring in a DSSC (from fs/ps for electron injection to ms for electron transport). Optical transient absorption techniques (see Chaps. 8, 14, 15) are used in combination with transient electrical measurements to follow the appearance and disappearance of chemical species and charges on a DSSC [27]. 

In essence, a DSSC device is composed of a transparent photoactive anode and a photo-inert counter electrode (cathode) sandwiching an electrolyte-containing redox mediator (Figure 6.1(a)). Conceptually, the device is based on the superposition of active layers whose thicknesses are 10- to 20-fold less than that of crystalline silicon wafers. Moreover, the requested purity of materials is 10-100 times less than for a silicon device. 

The much simplified picture of the energetics and kinetics for a working DSSC device, which emerged in the early research,is still useful as an introduction of working principles. The chemical complexity of the device must, however, be understood and mastered to improve our ability to identify predictive materials and optimised structure/function relation-ships. The present understanding of these processes is now covered with specific emphasis on the electron transport through the mesoporous TiOi electrode. The reader is also directed to recent review articles on these topics. 

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