Polymer Solar Cells

Currently, the active materials used for the fabrication of solar cells are mainly inorganic. Materials such as silicon (Si), gallium-arsenide (GaAs), cadmium-telluride (CdTe), and cadmium-indium-selenide (CIS). Nevertheless, the large production cost for the silicon solar cells is one of the major drawback in this field. This chapter is dedicated to a critical presentation of another type of photovoltaics, called polymer, or plastic, solar cell technology. Polymer solar cells have attracted significant attention in the past few years due to their potential of providing environmentally safe, lightweight, flexible, and efficient solar cells.

Analytical Models of Bulk and Quantum Well Solar Cells and Relevance of the Radiative Limit

The analytical modelling of bulk and quantum well solar cells is reviewed. The analytical approach allows explicit estimates of dominant generation and recombination mechanisms at work in charge neutral and space charge layers of the cells. Consistency of the analysis of cell characteristics in the light and in the dark leaves a single free parameter, which is the mean Shockley-Read-Hall lifetime. Bulk PIN cells are shown to be inherently dominated by non-radiative recombination as a result of the doping related non-radiative fraction of the Shockley injection currents. Quantum well PIN solar cells on the other hand are shown to operate in the radiative limit as a result of the dominance of radiative recombination in the space charge region. These features are exploited using light trapping techniques leading to photon recycling and reduced radiative recombination. The conclusion is that the mirror backed quantum well solar cell device features open circuit voltages determined mainly by the higher bandgap neutral layers, with an absorption threshold determined by the lower gap quantum well superlattice.

Prospects and Strategy of Development for Advanced Solar Cells

This chapter presents the necessity for developing high performance, low-cost, and highly reliable solar cells in order to further deployment of photovoltaics, as well as the prospects and strategies for developing advanced solar cells.

The Luminescent Solar Concentrator

Luminescent Solar Concentrators (LSCs) offer a way of making Photovoltaic (PV) systems more attractive through reduced energy costs, the possibility of application in cloudy regions, and improved building integration. LSCs collect light over a large area and concentrate it, both spatially and spectrally, onto solar cells at the edges of the device, such that the total cell area required to generate a specific power is reduced. Since the solar cells constitute the more expensive component in the system, this leads to cost reductions. Unlike conventional geometric concentrators, LSCs do not require solar tracking and can collect diffuse as well as direct sunlight. The current research challenges lie in increasing the efficiency of the LSC and extending it to larger areas to make it commercially viable. In this chapter, the authors outline the mode of operation of the LSC, with particular regard to cost considerations and device geometry. They then review recent approaches aiming to increase device efficiency and, finally, introduce their versatile raytrace approach to modelling the LSC. The model is utilised here to investigate tapered LSC designs and rationalise the optimal geometry and configuration for planar LSCs.

Phononic Engineering for Hot Carrier Solar Cells

In this chapter, the authors first analyse the operation of a hot carrier solar cell and lay down the general principles. They then discuss the opportunity of phonon engineering to improve the phonon bottleneck. Finally, they present how these can be modeled in nanostuctures comprising several thousand atoms, where true 3D phonon dispersion relations for Si-Ge nano-structures are obtained using first principles methods. The effects of the nano-structure size and geometry on the phonon dispersion relations are investigated. The possible phonon decay processes in the nano-structures are discussed and compared with the bulk crystal materials. The performance of calculated nano-structures on the hot carrier solar cell is evaluated with the acquired knowledge of phonon modes.

Quantum Dot Solar Cells

Advanced concepts for high efficiency solar cells such as hot carrier effects, Multi-Exciton Generation (MEG), and Intermediate-Band (IB) absorption in low-dimensional nanostructures are under focused research topics in recent years. Among various potential approaches, this chapter is devoted to the device physics and development of the state-of-the-art technologies for quantum dot-based IB solar cells.

Hybrid Solar Cells

Conventional solar cells are usually manufactured from silicon, an inorganic material. This type of solar cell has a high efficiency, up to 40%, but these cells are using very expensive materials of a high purity and energy intensive processing techniques. This chapter is dedicated to a critical presentation of hybrid solar cells. They are a combination of both organic and inorganic nanostructure materials and, therefore, combine the properties and advantages of their components. Unfortunately, so far, the hybrid solar cells have a low conversion efficiency of the sunlight, 6-7% (Kim, et al., 2007).

Organic Solar Cells Modeling and Simulation

Modelling and simulation of organic (polymer, dye sensitized, and nanotube) solar cells is discussed. High J-V theoretical curves, the calculation of key parameters, and also the relative influence of different parameters on the cell operation, are evidenced and analyzed. On this basis, the authors obtain information on the optimization of the solar cell design and manufacturing.

Quantum Confinement Modeling and Simulation for Quantum Well Solar Cells

In this chapter, the authors present the modelling and simulation of the multi-layered quantum well solar cells as well as the simulated results of this model. The quantum confinement of a semiconductor induces new energy levels, located in the band gap, as well as resonant levels located in the conduction and valence bands. These levels allow supplementary absorption in the visible and near infrared range. The quantum efficiency of the supplementary absorption is calculated within the infinite rectangular quantum well approximation. As the absorption excites carriers in the gap of each layer, even a small absorption significantly increases the photocurrent (by photoassisted tunneling) and, therefore, the cell efficiency. The results of the simulation are presented for the internal quantum efficiency of the transitions between the resonant levels of GaAs, as well as the internal quantum efficiency of the transitions between the confinement levels for GaAs and AlxGa1-xAs. New directions for the research of quantum well solar cells are indicated.

New Trends in Solar Cells

Photovoltaic (PV) power generation technology is one of the most promising renewable energy technologies because of the possibility of solving environmental problems and limited sources of energy. In order to realize widespread deployment of solar photovoltaics and contribute to further development in civilization, further development in the science and technology of PV is very important. That is, further improvements in conversion efficiencies and reliability and lowering the cost of solar cells and modules are necessary. Regarding conversion efficiencies of solar cells, because there is the Shockley–Queisser conversion efficiency limit of 31% at 1-sun and 41% under concentration for single bandgap solar cells, several approaches to overcome the Shockley–Queisser limit should be made. This book will provide readers some guidance to overcome the limit. This chapter presents the current status of solar cells and new trends in solar cells from the viewpoint of conversion efficiency.