Low temperature photovoltaic devices with quasi-epitaxial silicon thin films on granular silicon substrates.

摘要

Solar energy is commonly considered as the best choice to replace fossil-based energy sources. However, the current solar cell technologies are not affordable for high volume power generation. Currently, the solar energy is 3--5 times more expensive than the hydro or nuclear energy and in order to the solar energy as a part of our life the cost of solar energy must be slashed by a factor of 2--5. The base material and the fabrication technology account for about 50% of a stand-alone PV system. An efficient cost reduction is possible by reducing the cost of base material, fabrication technology and the associated electronic system.; This thesis tackles the cost of solar cells from material and device structure point of view. Thin-granular Si substrates obtained from low cost Si feedstock and low cost crystallization techniques were employed in this work as the base of the solar cells. The major achievements of this thesis are the development of a novel low temperature epitaxial Si emitter on granular Si substrates and the development of a new solar cell device structure without transparent conductive oxide.; The new thin Si films so called "quasi epitaxial (qEpi) films" doped with high concentration of phosphorous (>1020 cm-3) were obtained by plasma enhanced chemical vapor deposition technique. Ultra high conductivity emitters, comparable to the high temperature diffused Si emitters, were developed using qEpi-Si materials at 260°C-300°C. The film growth mechanism, electrical properties, and optical properties were assessed for photovoltaic application.; A new kind of low temperature Si solar cell and photodetector was introduced using the new developed qEpi-Si emitters. Due to the high conductivities of the qEpi-Si emitters, we were able to eliminate the transparent conductive oxide. The new process is fully PECVD compatible and has a good potential for industrial upscalability.