Photovoltaic Cells based on Conducting Polymers

Converting solar energy into electricity may provide a much-needed solution to the energy crisis the world is facing today. The high cost (and high energy consumption) involved in manufacturing crystalline silicon for inorganic solar cells hinders a major contribution of photovoltaics in energy production. Plastic solar cells, on the other hand, can provide low cost fabrication besides easy processing and mechanical flexibility. As such, they are the most promising cost-effective alternatives to silicon-based solar cells.

However, the power conversion efficiencies, PCE, of all reported organic photovoltaic devices are still very low in comparison to typical inorganic photovoltaic cells. After introduction of the bulk-heterojunction concept, the PCE of polymer/fullerene photovoltaics is nearing to 5%. But, these values are not sufficient to meet realistic specifications for commercialization. High photovoltaic efficiency requires efficient light absorption and transport of charge carriers. Polymers have much lower carrier mobility than inorganic semiconductors. The two main factors  contributing for low PCEs in plastic PVs are indeed the low mobility of the generated charges and the mismatch between the absorption of the polymer based devices and the solar spectra.

Previous attempts in our group to fabricate efficient photovoltaic cells based on anthocyanins and conjugated polymers met with problems pertaining to the difficulty of solubilisation of all anthocyanin and polymer pairs tested. On the other hand, on the cases were films were produced and tested, no photovoltaic activity was detected either due to the extremely low mobility of the excited electron, fast charge recombination or inefficient charge transfer.

One way to improve the PCE of working plastic PVs that use fullerene derivatives as electron acceptors is to improve the absorption of the solar radiation broadening the UV/Vis spectra using a polymer blend instead of a single polymer. Our work is now directed to developing more efficient bulk-heterojunction photovoltaic cells that use blends of polymers whose spectra allow an efficient solar light absorption.

Research Projects

Photovoltaic cells based on conducting polymers and anthocyanins POCI/CTM/58767/2004 (PI)