For successful thin film photovoltaics the charge transport of photogenerated charge carriers must be easy enough to accommodate the photocurrents generated. Optical absorption must also be strong enough to absorb the light impinging on a thin film, and the spectral match between the optical absorption of the photovoltaic material or device and solar spectrum should maximise photocurrent. Devices should be tolerant of narrow angles of incidence of light, polarised (eg reflected) light, low levels of light and light of different frequencies. There are big diferences here and some record breaking systems in ideal conditions can be very inferior in real world conditions.
The photovoltage generated should be at a minimum to ensure that the energy conversion loss is minimized. There are trade offs between several of these conditions, in particular for the spectral matching the photovoltage extracted and the optical absorbance in thicker devices versus transport without excessive losses. In addition certain applications benefit from the cells converting heat as well as light into electricity ie they are "thermophotovoltaic." Other applications benefit from tolerance of low light levels and low angles on incidence. Traditional silicon is poor at all these things.
Work on inorganic thin film photovoltaic devices beyond crystalline and amorphous silicon is now wide ranging, both geographically and in topic. For example, the University of New South Wales in Australia is working on silicon quantum dots in a dielectric matrix. Graz University of Technology in Austria researches ZnS nanoparticles in photovoltaic devices and Ioffe Physico-Technical Institute in Russia develops thermophotovoltaic cells and modules based on GaSb. All of them present at the 22nd European Photovoltaic Solar Cell Conference in Milan, Italy in September 2007. This is an academic conference.
For Background read the reports Printed Photovoltaics and Batteries and Inorganic Printed and Thin Film Electronics.
For commercialisation of printed and thin film electronics attend Printed Electronics Asia 2007 or Printed Electronics USA 2007
Source top image: fotosearch.com
