Bradforth Research Group
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Nanoparticle/Polymer Hybrid Solar Cell Photophysics
Jimmy Joy and Saptaparna Das


Third-generation photovoltaic materials are designed to efficiently absorb the sunlight and convert it to electricity at low cost. Bulk heterojunction hybrid solar cells are comprised of semiconductor nanocrystals blended with conjugated polymers. These hybrid solar cells have demonstrated improved photovoltaic device performance over the past 12 years. The semiconductor nanocrystals in the hybrid cells offer spectral tunability through quantum confinement effects, high dielectric constants, and high electron mobilities when compared to commonly used fullerene acceptors. While the design of hybrid systems are being developed to further enhance the efficiencies of these solar cells, the physical mechanisms that occur at the hybrid interfaces are still poorly understood, in particular the formation and evolution of charge transfer states and of mobile charge carriers.

We are characterizing the electron transfer dynamics and electron transfer yield in hybrid BHJ blends consisting of P3HT and related polymers with CdSe nanocrystals by using spectrally resolved Transient Absorption and Time Correlated Single Photon Counting spectroscopy. Our collaborators, the Brutchey group can define the surface functionalization of the nanoparticles and spectroscopy lets us identify excited states and track the dynamics of separated charges in the femtosecond to microsecond time range.

Transient absorption spectra of a hybrid film and of its individual components. The 600 nm negative feature comes from reduced nanocrystals (CdSe QDs, in yellow) and rises within 65 fs.