Optical analysis of subbandgap defects in polycrystalline silicon thin film solar cells

Subbandgap defects in polycrystalline silicon thin films are investigated using photothermal deflection spectroscopy and photoluminescence. By applying rapid thermal annealing and hydrogen passivation, samples of different material quality are fabricated. An increasing defect absorption with increasing annealing temperature was measured, although the open circuit voltage of the respective solar cells was improved. The results are compared to photoluminescence and Raman spectra. An inverse correlation between the radiative and non-radiative recombination processes in the subbandgap energy regime was found. Raman measurements show that the structural order is disturbed by hydrogen passivation, although the material quality is improved. These contradictory trends show that an investigation by solely one of these characterization methods is not suitable for determining the material quality of solid phase crystallized poly-Si thin films.