Reducing cost and improving conversion efficiency are the main tasks in order to make photovoltaic energy competitive and able to substitute traditional fossil energies.Nanotechnology seems to be the way by which photovoltaics can be developed, whether in inorganic or organic solar cells. Wide-bandgap nanostructured materials (nanomaterials) prepared from II-VI and III-V elements are attracting an increased attention for their potential applications in emerging energy. They can be prepared in different geometric shapes, including nanowires (NWs), nanobelts, nanosprings, nanocombs, and nanopagodas. Variations in the atom arrangements in order to minimize the electrostatic energy originated from the ionic charge on the polar surface are responsible for a wide range of nanostructures.This book chapter will focus on contribution of nanomaterials in solar cell technology advancement.
KeywordsNanomaterials; Solar cells; Organic; Inorganic; Nanopillars; Nanowires; Nanobelts; Nanorods; Photocarrier collection
IntroductionSolar cells have known a big expansion these last years due to the voluntary move to cleaner energies like photovoltaics. Table 1 summarizes the chronological evolution of photovoltaic cells with their main characteristics. After solid-state physics has shown its limits by reaching the maximum possible conversion efficiency for silicon, CdTe, and CuInSe 2, the highest conversion efficiency was obtained for triple-junction compound InGaP/GaAs/InGaAs solar cell with 37.9 % [6]. Chemistry seems to be another way by which an increase of the solar cell conversion efficiency is possible. Nanomaterials made by chemical ways present high opportunity in efficiency enhancement by increasing light trapping and photocarrier collection without additional cost in solar cell fabrication.The physical and chemical properties change from the bulk material to the nanomaterial. As an example, the melting point is lowest for the nanomaterial compared to its bulk one. This can be due to the high surface-to-volume ratio of atoms in a nanoparticle [7].The main nanomaterial physical property is the large surface-to-volume ratio [6] due to different forms created; nanowires [8,9], nanopillars [10,11], nanocones [12], quantum dots [13].It has been shown that light trapping is due to the increase of the photon path inside nanostructures [14][15][16] which enhance the electron-hole pair creation probability. Quantum dots (QDs) have the particularity to have a size-dependent bandgap [13,17,18] so it can be adjusted to fit the maximum solar spectrum.
Classical Solar CellsBefore introducing the added value of nanomaterials in solar cells, a brief comeback should be presented to understand the work mechanism of solar cells.A solar cell is an electronic device, a P/N junction in its basic form, which has the ability to convert sunlight into electricity. This phenomenon was discovered by Edmond Becquerel in 1839 and is called the photovoltaic effect [19].Not all materials can be solar cell components. Because the main feature sho...