| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Tuesday Sessions |
| Session EN+TF-TuA |
| Session: | Thin Films for Photovoltaics |
| Presenter: | S.Y. Chiam, Institute of Materials Research & Engineering, Singapore |
| Authors: | S.Y. Chiam, Institute of Materials Research & Engineering, Singapore S.J. Wang, Institute of Materials Research & Engineering, Singapore J.S. Pan, Institute of Materials Research & Engineering, Singapore L.M. Wong, Institute of Materials Research & Engineering, Singapore W.K. Chim, National University of Singapore |
| Correspondent: | Click to Email |
It is important to investigate new materials for thin film solar cells for 2nd generation devices. Materials extraction cost and annual electricity production considerations highlighted several potential new materials including cuprous oxide (Cu2O). In this work, we report on the growth of Cu2O and highlighted the importance of the oxygen partial pressure during growth. Namely, the partial pressure of oxygen determines the transition of Cu2O to CuO with increasing partial pressure. This is accomplished at a fixed total pressure as this may influence Cu2O formation. We then discuss about the interface energy alignments, first between between Cu2O/ZnO and then ZnO/Si. The former is of importance as inorganic thin film p-n junction that is suitable for 2nd generation solar cell devices. For the latter case, we fabricated device structure on differently doped Si, to investigate influence on doping on the transport characteristics of the hetero- pn junction. It is found that forward bias characteristics for a heterojunction, is not critically dependant on the band offsets, but rather the build-in-field at the heterojunction. If the physics is considered from the point of view of quais-fermi level separation during light illumination, this build-in-field will also determine the Voc. In this sense, band offset measurements can only give an indication of the maximum limit of the Voc for differently doped semiconductors (non-degenerate) heterojunction solar cells. In addition, we show that under illumination, the current conduction for the ZnO/Si at zero-bias is a “forward bias” current, unlike all homojunction devices. This can be understood with a detail examination of the energy band diagrams. This work shows the importance of using measured band offsets to aid in understanding the relative Fermi-level alignment instead of using bulk electron affinity values. The work also demonstrates a whole array of playground possible for thin film heterojunction of different materials to engineer an ideal junction for solar cell devices.