State-of-the-art Spectroscopic Investigation

The insight into the native photophysics of the energy materials are obtained by employing the ultrafast pump−probe spectroscopy and probing the transients in the visible region of the spectrum. The femto-second ultrafast spectroscopy technique is used to study photoinduced dynamical processes in atoms, solids and nanostructures. The carrier dynamics of charges, excitons and phonons control the properties of a range of energy materials. Ultrafast laser spectroscopy involves studying the ultrafast events that take place in a medium using ultrashort pulses and delays for time resolution. In our recent investigations, we studied various energy materials using transient spectroscopy and our findings provide new insights into the fabrication of the cost-effective photovoltaic devices based on CZTS and SnSe-based heterostructures.

SnSe/CdSe Heterostructures: Transient absorption (TA) studies demonstrate a drastic enhancement of the CdSe biexciton signal which points toward the hot carrier transfer from SnSe to CdSe in a short time scale. The fast growth and recovery of CdSe bleach in the presence of SnSe indicate charge transfer back to SnSe. The observed delocalization of carriers in these two systems is crucial for an optoelectronic device.

CZTS/CdS Heterostructures: We monitored the ultrafast charge carrier dynamics in the junction and confirmed the efficient separation of photoexcited charge carriers in the CZTS/CdS heterojunction. In the CZTS/CdS heterojunction, the photoexcited electrons are transferred from CZTS to CdS, which results in a drastic increment of the bleach signal intensity compared to that of bare CdS. Similarly, the photoexcited holes are transferred from CdS to CZTS, monitored by steady-state and time-resolved spectroscopy. A slower bleach recovery confirms the spatial charge separation at the interface of the CZTS/CdS heterojunction, placing electrons and holes at CdS and CZTS, respectively.