Nano- and Molecular Precursors for CdTe Photovoltaics

Solution-processable semiconductors offer the potential for inexpensive and high-throughput processing of photovoltaics with high materials utilization.  One approach that has been used to successfully produce high efficiency solar cells is to use solution-deposited materials as a nanocrystalline or molecular semiconducting thin film that can be annealed into a large-grained material.  We report approaches to producing crystalline CdTe films using nanocrystals capped with either pyridine or metal-chalcogenide complexes (MCCs) as well as MCCs alone.  We find that with low temperature  (~350°C) sintering in air, the grain size can be increased from ~5 nm to over 100 nm.  Out best solar cells show high short circuit currents (~24 mA cm^-2) but low open circuit voltages (~600 - 700 mV).  Additionally, the devices require current and/or light soaking to achieve their maximum efficiency.  In optimized devices, power conversion efficiencies of up to 9.7% have been achieved in a ITO/CdTe/ZnO/Al configuration.  We find that the efficiency may be limited by non-ideal contacts and offer some insight into ways the open circuit voltage could be improved.