Introduction to inorganic thin film solar cells

Solar energy represents the largest energy input into the terrestrial system. Although photovoltaics is not the sole answer to the myriad of energy challenges offered by the clean and economical use of sun spectrum, this renewable energy option can make an important contribution to the economy of each country. Despite its relatively low power density, the solar electricity market is booming. By the end of 2007, the cumulative installed capacity of solar photovoltaic (PV) systems around the world had reached more than 9,200 MW. This compares with a figure of 1,200 MW at the end of 2000. Installations of PV cells and modules around the world have been growing at an average annual rate of more than 35% since 1998. The EPIA/Greenpeace Advanced Scenario [1] shows that by the year 2030, PV systems could be generating approximately 2,600 TWh of electricity around the world to satisfy the electricity needs of almost 14% of the world’s population Photovoltaics stumbling block has always been its cost but it has held the promise of providing clean electricity and competitive rates. The cost is declined by a factor of nearly 150-160 times since the invention in 1954 of the modern solar cell based on crystalline silicon technology. More then 90% of the current production uses 1st generation PV wafer based cSi (1st G PV) a technology with the ability to continue to reduce its cost at its historic rate. The direct production costs for crystalline silicon modules are expected to be around 1 €/Wp in 2013, below 0.75 €/Wp in 2020 and lower in the long term as indicated in table 1 [5]. Thin-film deposited directly on large area substrates, such as glass panels (square meter-sized and bigger) or foils (several hundred meters long) in roll-to-roll application, recognized as 2nd generation approach (II G) is always looked at as the “younger cousin” of the silicon technology, as pointed out by L.L Kazmerski [3]. It has an inherent low-cost potential because it requires only a small amount of expensive photo-active materials and its manufacture is suited to fully integrated processing and high throughput with a very low energy pay back time (<1.0 year or less). It poised to take over the energy production responsibilities of its older relative but it never quite fulfilling its expectations or potential except during last year when its market share moved from 6 to over 10%. during 2005- 2008– period (chapter 1 this book ) the higher growth rates of the whole PV industry. The fantastic boom of thin film technology, during last years, can suggest further development principally during next years mainly due to the application of innovative concept to conventional materials and new class of thin film material coming from nanotechnologies, photonics, optical metamaterials, plasmonics and new semiconducting organic and inorganic sciences, all them recognized as 3rd generation approach (3rd G PV) to overcome efficiency limitation at low cost [15]. Within the next 20 years, it is reasonable to expect that 2nd G PV technologies cost reductions and the implementation of some new technologies and introduction of high efficiency 3rd G PV concepts can lead to long term fully cost-competitive solar energy based on thin film approach. First, second and third generation PV are mainly based on inorganic approach. They cover a very wide area of material science and only a short overview can be outlined in this introduction leaving to the reader to analyse thoroughly the introduced concepts in the remaining part of the book as well by consulting a very wide available bibliography partially indicated in the references of each chapter.