In situ studies of transient photoconductivity in PbSe quantum dot solar cells

PbSe quantum dot (QD) solar cells have attracted significant interest due to their band gap tunability, easy-processing and flexibility. Efficiencies have risen from 1{\%} just a few years ago to nearly 9{\%} today. Furthermore, the novel concept of multiple exciton generation (MEG) resulting from quantum confinement makes these materials scientifically interesting counterparts to bulk semiconductors. Recent observations of more than 100{\%} external quantum efficiency in PbSe QD solar cells confirm direct relevance of MEG to practical photovoltaics. However, in order to take full advantage of this effect, one needs a better understanding of photogeneration dynamics and carrier transport in QD solar cells. In this talk, we discuss a new technique for in situ measurements of transient photoconductivity with fast response time (\textless 50 ps) applied to study carrier transport and photogeneration dynamics in PbSe QD solar cells. These measurements complement traditional photoconductivity techniques such as time-resolved microwave conductivity and time-of-flight. Based on the analysis of temperature, excitation wavelength and electrical field dependence measurements, we derive parameters such as MEG efficiency, carrier lifetime, trap-free mobility and carrier emission rate from trap states.