**1. Introduction**

The global energy demand has been continuously increasing due to the continuous growth of the world population, economic development, standard of living, and drive of modern technologies. In the current situation, about 87% of the primary energy needs are mostly supplied through fossil fuels (coal, oil, and gas) [1, 2].

However, the sources of these fossil fuel reserves are depleting very fast. The existing sources of energy are inadequate, and if the fuel consumption continued at current usage rates, it would last only about 50 years [3]. On the other hand, burning fossil fuels releases carbon dioxide and other greenhouse gases (e.g., water vapor, methane, nitrous oxide, sulfur dioxide, and other ozone-depleting substance) in the atmosphere, making them the primary contributors to global warming and climate change. Because of the depletion of fossil fuels and global warming, in recent years, researchers are endeavoring severe attempts to find out various ways to meet energy demand around the world. Renewable energy could be an eco-friendly, alternative, sustainable energy resource because they are inexhaustible and will not pollute the environment for us or those of future generations by emitting harmful gases. Many alternative renewable energy sources have already been available, such as solar, hydro, wind, biogas, biomass, geothermal, wave, and tidal energy. Among all renewable resources, solar energy can be the solution to the problem of dwindling fossil-fuel reserves [4].

choice of the extracting solvents and the dye mixture's at proper volume ratio, enhancing the dye sensitizer's inherent properties, such as absorption and adsorption, thus improving the cell efficiency. Section 4 explains the comprehensive study of the blocking layer and its effect on the cell efficiency, and finally in section five, overall conclusions and accomplishments of this study have been mentioned.

*Effect of Combination of Natural Dyes and the Blocking Layer on the Performance of DSSC*

As shown in **Figure 1**, a typical DSSC consists of five different parts, such as, (1) transparent conducting oxide (TCO), glass substrate, (2) anode (wide band-gap semiconductor material layer on TCO), (3) photosensitizer, (4) electrolyte and (5) cathode (platinum/carbon layer on TCO). The components of a DSSC are: two transparent conductive oxide [indium tin oxide (ITO), fluorine-doped tin oxide (FTO), Indium Zinc Oxide (IZO) and Aluminum Zinc Oxide (AZO)] glass electrodes. One of the electrodes is the anode, the working anode, which is printed with

semiconductor material [TiO2, ZnO, SnO2, SrTiO3, Zn2SnO4, Nb2O5, etc.]

working electrodes is the electrolyte containing the redox couple [I/I3

and SeCN/ (SeCN)3

nanoparticles (particle size around 20–50 nm). The semiconductor oxides are sensitized with a photosensitizer (metal complex sensitizer, metal-free organic sensitizer or natural dye sensitizer), which absorbs the photons. The other electrode is the counter electrode [platinum or carbon coated TCO] and in between the two

, etc.]. **Figure 2** illustrates the schematic diagram of the basic working principle of a typical TiO2 based DSSC. All other semiconductor-based DSSC such as ZnO, SnO2, etc. works under the same principle. Under illumination, a photo-excited electron is injected from the excited state of the dye (D\*) from the highest occupied molecule orbital (HOMO) to lowest un-occupied molecular orbital (LUMO) (Eq. (1)). The excited electron is injected to the conduction band of the semiconductor material. The injected electron percolates through the semiconductor material by a driving chemical diffusion gradient and is collected at the TCO glass substrate (Eq. (2)). After passing through an external circuit, and reaches the counter electrode, thus,

, Br/Br3

,

**2. Basics of DSSC**

*DOI: http://dx.doi.org/10.5772/intechopen.94760*

SCN/ (SCN)3

**Figure 1.**

**315**

*Schematic diagram of basic structure of DSSC.*

Solar energy is the cleanest and most abundant renewable energy source available. The solar cell or photovoltaic (PV) device is used for converting the energy of sunlight into useable electrical energy. The generated energy from solar does not produce any harmful emissions, consumes no fossil fuels, has no moving parts, and requires little maintenance. The development of PV technology is growing, and intensive research works are undertaken worldwide to improve cell performance and reduce the cost of the cell. With a history dating back over 60 years, since the very first silicon bipolar solar cell, the last three decades silicon solar cell has seen immeasurable advancement in both the performance of experimental and commercial cells. First-generation silicon solar cells showed their value in the market with the advantages, including high efficiency (26.6%), high reliability, low cost, ease of fabrication, and environmentally friendly traits [5–8]. Second generation thin-film (e.g., amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS)) solar cells are cheaper than the mature Si solar cells; additionally, thin-films are easier to handle and more flexible. However, the shortage of Tellurium and Indium makes it hard to manufacture solar cells commercially. Also, Cadmium is extremely poisonous and medical problems with environmental impact [9]. This significant concern opened the method of exploration of finding other elective materials and further innovation for solar cells. Several new thinnerfilms have surfaced through concentrated research with higher potential, including dye-sensitized solar cell (DSSC), perovskite solar cell (PSC), copper zinc tin sulfide (CZTS) solar cell, organic solar cell (OSC), and quantum dot solar cell (QDSC) [10].

The DSSC belongs to the group of thin-films, functions on a semiconductor generated into an electrolyte and a light-sensitive anode [11]. In 1988, Brian O'Regan and Michael Grätzel at UC Berkeley, USA initially co-invented the modern version of DSSC and later they further developed this work at the ÉcolePolytechniqueFédérale de Lausanne, Switzerland [12]. Brian O'Regan and Michael Grätzel reported the first modern version of DSSC in 1991 with an efficiency of 7.1–7.9% [13, 14]. DSSC can convert the solar energy to electrical energy by using photosensitive dye. DSSC is fabricated by using conventional roll-printing systems. The semi- transparency and semi-flexibility of DSSC offer a diversity of usages not appropriate for glass-based construction and most of the materials used are lowcost. However, practical elimination of several expensive elements has proven to be difficult, notably Pt and ruthenium (Ru). The energy conversion efficiency of the most recent laboratory-developed module is approximately 14.7% [15]. This chapter is focused on the improvement of efficiency of DSSC by the combination of natural dyes and the blocking layer. In this work, structure and operation principle of the third generation dye-sensitized solar cell (DSSC) has been discussed in the second section. Section 3 explains the combination of natural dyes with an optimized

*Effect of Combination of Natural Dyes and the Blocking Layer on the Performance of DSSC DOI: http://dx.doi.org/10.5772/intechopen.94760*

choice of the extracting solvents and the dye mixture's at proper volume ratio, enhancing the dye sensitizer's inherent properties, such as absorption and adsorption, thus improving the cell efficiency. Section 4 explains the comprehensive study of the blocking layer and its effect on the cell efficiency, and finally in section five, overall conclusions and accomplishments of this study have been mentioned.
