Integration of CdTe-ZnO nanocomposite thin films into photovoltaic devices

Quantum-scale semiconductor nanoparticles offer unique, size-dependent optical and electronic properties of import to enhanced photovoltaic conversion efficiency. The present study addresses the integration of CdTe nanocrystal assemblies, used as spectral sensitizers, into thin film photovoltaic heterojunction devices. CdTe nanocrystals, embedded in an electrically active ZnO matrix, form a nanocomposite offering control of both spectral absorption and photocarrier transport behavior through the manipulation of nanophase assembly (ensemble effects). A sequential RF-magnetron sputter deposition technique affords the control of semiconductor nanophase spatial distribution relative to the heterojunction plane in a hybrid, ZnO-P3HT test structure. Energy conversion performance, (J-V and quantum efficiency (QE) response) was examined as a function of the location of the CdTe nanophase absorber region using both 1-D device modeling (SCAPS) and the experimental examination of analogous P3HT-ZnO based hybrid thin film devices. Enhancement in simulated QE over a spectral range consistent with the absorption region of the CdTe nanophase (i.e. 400-475 nm) is confirmed in the experimentally determined external quantum efficiency (EQE). Moreover, a trend of decreasing efficiency in this spectral range with increasing separation between the CdTe nanophase region and the heterojunction plane is observed. The results are interpreted in terms of carrier scattering/recombination length mitigating the successful transport of photocarriers across the junction.