Characterization of thin-film a-Si:H/μc-Si:H tandem solar cells on glass substrates

Techniques, such as photoluminescence (PL) and electron-beam-induced current (EBIC), have already proven their effectiveness and applicability for solar materials. Although, the methods are standard techniques for multicrystalline Si PV, their application to thin films is challenging and requires special adjustment and a careful selection of the measuring parameters. Here we report on the investigation of thin-film tandem solar cells consisting of hydrogenated amorphous (a-Si:H) and microcrystalline silicon (mu c-Si:H) on glass substrates. We observe a homogeneous spatial distribution of the PL signals caused by the dominance of the surface recombination. A typical PL spectrum exhibits sub-band gap features of a-Si:H. We relate the sub-band-gap spectral features mainly to transitions of carriers trapped in deep states. Observations on partially processed stacks support this supposition. PL is only detectable on the a-Si:H layer, while EBIC signal is generated mainly in the mu c-Si:H layer. It is found out that the luminescence features of the thin a-Si:H layer resemble those on bulk a-Si:H.