Electron hybrid semiconductor nanocrystals

Semiconductor NCs are composed of hundreds of unit cells and each cell has a HOMO (highest occupied molecular orbital) and a LUMO (lowest unoccupied molecular orbital). Taken together, these form valence and conduction bands, respectively. In the case of CdSe nanocrystals (NCs), an sp hybridized semiconductor, 4p orbitals in Se form the valence band, while the conduction band is comprised of 5s orbitals in Cd. A single electron excitation from the highest occupied valence band to the lowest unoccupied conduction band creates an j-type excited electron and a p-type hole. ... 

In bulk (or dispersed) heterojunctions, nanocrystals are blended into the polymer to create a heterogeneous composite with a high interface surface area. In this hybrid solar cell concept, photo induced charge separation is favored between high electron affinity inorganic semiconductors and relatively low ionization potential polymer. The maximum power conversion efficiency has reached 2.8 % under AM 1.5 illumination condition by using the composite of tetrapods of CdSe nanocrystals and MDMO-PPV [4], while the PCE of the device based on the composite of CdTe nanorods and MEH-PPV is only 0.052 % in similar conditions [5]. 

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