In the last decade, the fast increase of the global energy consumption, mainly related to the strong economic growth in the Far East, and the progressive depletion of the fossil fuels induced a run-up in the world oil price. Both these economic concerns and the growing global pollution pointed out that a transition toward renewable energies is mandatory. Among renewables, the conversion of sunlight into electricity by photovoltaic (PV) devices is a reliable choice to cope the growing energy consumption, due to the huge potentially extractable power (up to 120000？TW). The most important classes of inorganic PV devices developed in the last sixty years will be reviewed in this paper, in order to depict the state of the art of the technologies which dominate the PV market. Some novel concepts which could have an important role in the future of PV will be also described. 1. Introduction Among renewable energies, the conversion of sunlight into electricity by photovoltaic (PV) devices is a reliable choice to tackle the growing global energy demand. In fact, the amount of solar energy reaching the surface of the Earth every hour can fully supply the global energy consumption over an entire year. Indeed, although a higher efficiency to cost ratio is required for the installed PV devices to make them competitive with the conventional energy resources, great strides were made in the last 30 years both in terms of installed PV power and cost reduction (see Figures 1(a) and 1(b)) [1–3]. Figure 1: (a) Global PV capacity from 1995 to 2011. Data from [ 1]. (b) Module average selling price in 1975 and from 1995 to 2011. Data from [ 2, 3]. Inorganic materials dominated the PV market from the beginning. Crystalline silicon (c-Si) solar modules are the most diffused PV devices, due to the peculiar properties and unique advantages of Si with respect to other PV absorbers (namely, availability, long lifetime, and sustainability). PV devices that compete with Si either in terms of reduced cost of production (i.e., inorganic thin films-based devices and organic solar cells) or in terms of improved efficiencies (e.g., concentrated PV systems based on III-V compounds) are emerging. Nevertheless, the PV market share of c-Si devices was 83% in 2011 versus 17% for all thin films technologies (namely, amorphous silicon, CdTe, and Cu(In,Ga)Se2). Organic PV devices are instead in the state of advanced development and pilot production [4]. Even if their commercialization started for indoor and low-power applications, they show efficiency, stability, and lifetime not yet comparable
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