Recent advances in understanding of a-Si:H based materials and performance of their solar cells

A brief review is presented of some recent results which shed new light on the nature of gap states and the microstructure of high quality a-Si:H materials which can be directly related to improved performance and stability of their solar cells. These results demonstrate that charged, and not just the neutral dangling bond D°, defects have to be included in assessing the quality and stability of a-Si:H for solar cells. It is also shown that the commonly used measurements and their interpretation, solely in terms of neutral dangling bonds and their densities, are inadequate and measurements are discussed which allow the contributions of charged defect states to be evaluated. Recent results are also presented and discussed in which the effects of hydrogen dilution on the growth and microstructure of a-Si:H materials have been characterised using real-time spectroscopic ellipsometry. Guided by the derived deposition phase diagram for these materials, systematic studies could be carried out on p-i-n solar cell structures which have provided insights into the properties of these materials and a systematic approach for improving performance and stability of their solar cells.