Challenges in microcrystalline silicon based solar cell technology

This contribution discusses recent scientific and technological challenges for the development of highly efficient microcrystalline silicon (μc-Si:H) based thin film solar cells. Aluminium doped ZnO films prepared by sputtering and post deposition etching serve as transparent conductive oxide (TCO) material, which provide excellent light trapping properties. Challenges are the transfer of this approach to cost-effective reactive sputtering from metallic targets and the reduction of optical absorption losses in the front TCO films. We developed μc-Si:H i-layers by plasma-enhanced chemical vapour deposition (PECVD) using 13.56 and 40.68 MHz excitation frequency, high deposition pressures and high RF-powers. These conditions provide sufficiently “soft” deposition for the growth of high quality μc-Si:H material and yield high deposition rates. Stable aperture area module efficiencies of 10.1% and 8.1% were obtained for a-Si:H/μc-Si:H and μc-Si:H modules, respectively, on 10 × 10 cm 2 substrate size. Subsequent up-scaling to ∼1 m 2 coating area was performed and a-Si:H/μc-Si:H modules exceeding 10% initial aperture area efficiency were obtained. We discuss the questions of process stability and process reproducibility with respect to large area PECVD production systems.