Photovoltaic Power Generation: The Impact of Nano-Materials

Solar power is seen by many as a solution to the world’s energy problems. The earth receives 1.7x1017W from the sun compared to a total electricity generation capacity of 4.6x1012W (OECD prediction for 2010). However the average power density is low with a daytime average over the earth of 680Wm-2. This makes centralised generation problematic but distributed photoelectric generation by domestic and commercial users is a rapidly developing market. However typical commercially available modules have an energy conversion efficiency of less than 12%. Silicon cells with 24% efficiency have been produced in the lab while multi-junction tandem cells using different semiconductor materials (GaInAs, GaInP and Ge) to absorb different parts of the sun’s spectrum have reached 40%. This chapter describes some of the materials and device achievements so far and looks at possible ways in which higher efficiencies might be achieved with particular emphasis on nano-materials to use more of the solar spectrum efficiently. The possibility of using quantum slicing and multiple exciton generation to make more efficient use of high energy photons is considered and impurity band generation as a possible route to use low energy photons. One of the greatest challenges is to do this cheaply using semiconductors made from non-toxic abundant elements.