Variable temperature double-optical-modulation apparatus

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Harvesting solar energy is a key endeavour for this century as we face ever-decreasing fossil fuel world reserves and ever-increasing environmental crises emanating from greenhouse gas production. Solar cell technology is currently based on silicon. Devices used for human energy consumption yield solar power conversion efficiencies of around 10%, which is sufficient to meet a significant fraction of energy demands in the industrialised world, but manufacturing such devices costs too much energy and produces greenhouse gases. In order to recover such energetic costs, up to four years of continuous operation are required. This is a significant fraction of the device lifetime; given the processing costs of silicon solar cells, it represents a serious obstacle to widespread implementation of this technology. In order for solar energy to have a more substantial impact on our energy requirements, we need to find alternative technologies that reduce energy payback periods and device processing costs. This research programme focuses on conjugated polymers, which now provide a technologically viable class of solution-processable, film-forming semiconductors. Organic photovoltaic diodes (OPVDs) currently receive considerable interest as candidate devices for this technology. The best materials that have been developed over the last decade show promise but OPVD power conversion efficiencies under solar illumination, measured routinely by numerous research groups, are currently limited to 5%. Detailed understanding of electronic dynamics is critical to surpass this efficiency limit. Our objectives are to measure processes that are important in electronic applications of organic solar cells. We will do so by inducing optical absorption with a photomodulated, tunable light source, and measuring very small changes in the optical transmittance of a photomodulated probe light source through the sample, induced by the pump light, as a function of temperature and modulation frequency. Understanding electronic processes in these new and exciting materials is essential for further development of organic electronics beyond incremental optimisation of materials and device parameters.