The challenges of organic solar cells

fossil fuel reserves is causing major changes in atmospheric carbon dioxide and associated climate change. Clearly, this is an untenable situation and alternative renewable energy sources must be found. The concept of harvesting the sun’s energy to create electrical power is an obvious answer and the principles of ‘photovoltaics’ (PV) (the direct conversion of ‘photons to volts’) have been demonstrated and understood for more than a century (since A.E. Becquerel’s work in 1839). Solar cells based on silicon semiconductor junctions remain the dominant photovoltaic technology. Silicon PV module arrays are commonplace on roofs in many countries around the world (although sadly not to the same extent in Australia, the country with more solar resources than any other industrialised nation). Other inorganic semiconductor materials such as GaAs, CdTe, CIGS (copper–indium–gallium–selenide) are challenging the silicon dominance, and non-silicon technologies will probably occupy more than 20% of the market by 2012. The basic success criteria for PV technologies are simply the $/watt cost of the electricity derived from the solar cell, the energy and economic payback (i.e. how long it takes to pay back the energy and dollars used to produce the solar cell and ancillaries), the lifetime and performance stability and, finally, the environmental impact of production and disposal (for example, you clearly cannot dispose of a CdTe PV module in landfill). Viable next-generation technologies must exceed current silicon performance on one or more of these value criteria.