| AVS 59th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM+TF-WeM |
| Session: | Hybrid Electronic Materials and Interfaces |
| Presenter: | J. Xue, University of Florida |
| Authors: | J. Xue, University of Florida R. Zhou, University of Florida P.H. Holloway, University of Florida |
| Correspondent: | Click to Email |
Hybrid photovoltaic (PV) cells based on conjugated polymers and colloidal inorganic semiconductor nanoparticles have attracted significant attention as an alternative for all-organic solar cells. However, so far the highest efficiencies for hybrid PV cells have been limited to 2-3%, significantly lower than that of all-organic PV cells. One main reason for the lower performance is attributed to the complex interfaces and surfaces involving the inorganic nanocrystals.
Here we report our recent work that significantly improves the efficiency of hybrid PV cells to the 5% level. First, a 30-70% increase in the device efficiency was achieved by incorporating a solution-processed ZnO nanoparticle layer between the active layer and the cathode. This was attributed to a combination of electronic, optical, chemical, and morphological effects, including blocking leakage of photogenerated holes to the cathode, optimizing the optical intensity profile in the hybrid active layer, minimizing recombination or quenching of photogenerated excitons and charge carriers. Maximum power conversion efficiencies of 2.5% and 3.5% were achieved with a high-gap polymer P3HT and a low-gap polymer PCPDTBT, respectively. The incorporation of the ZnO nanoparticle layer also drastically improves the stability of the hybrid PV cells.
We further demonstrated another 30-50% improvement in the efficiencies of hybrid PV cells by treating the hybrid active layer in an acetonitrile solution with 1% ethanedithiol (EDT). This leads to a maximum efficiency of ~5.0% for the EDT-treated hybrid PV cell with a PCPDTBT:CdSe nanorod active layer. Detailed characterizations of the hybrid active layers before and after the EDT treatment revealed no appreciable differences in their morphology and absorption spectra; however the phosphonic acid organic ligands on CdSe nanocrystals are more completely removed, and an improved electron mobility was obtained upon EDT treatment. We attribute the enhanced efficiency to more complete removal of exciton/charge recombination centers and the subsequent atomic layer passivation of the CdSe nanorod surface.