Charge transfer in solar cells: Connecting the dots
Solar cells based on quantum dots have offered an attractive option for photovoltaics as they can be easily made to absorb different parts of the solar spectrum and are cheap to manufacture. Efficiency of such solar cells can be limited by charge transfer that is susceptible to losses occurring at interfaces between different materials. Within the project POLYDOT (Control of the electronic properties in hybrid- quantum dot/polymer-materials for energy production), scientists overcame the difficulties encountered in current methods of obtaining detailed experimental information about charge transfer. The new advanced methods of studying interfacial charge transfer recombination processes included photo-induced charge extraction and photo-induced transient photovoltage. These enabled the POLYDOT team to measure charge recombination in quantum dot solar cells at 1 sun or 100 mW/cm2 of irradiance and to measure the accumulated charge at different illumination conditions. POLYDOT shed further light into charge transfer reactions and their influence on certain solar cell parameters that have been largely overlooked. For example, it explored the impact of non-geminate recombination reactions on the final open circuit voltage and the impact of electric fields in bilayer cells with quantum dots and organic semiconductor materials such as fullerene. Project work contributes to enhanced understanding of charge transfer reactions that control the device's photocurrent, photovoltage and fill factors. These allow identifying the relationship between device efficiency and charge transfer mechanisms, and ultimately to obtain optimised solar cells with conversion efficiencies close to the maximum value.
Keywords
Charge transfer, solar cells, light absorption, quantum dot, POLYDOT
