Correlations between structural properties and performance of microcrystalline silicon solar cells fabricated by conventional RF-PECVD

In this study, direct structural characterization of μc-Si:H solar cells deposited by conventional RF-PECVD was conducted using Raman spectroscopy, XRD, and AFM. Strong correlations between i-layer structural properties and device performance were established. A wide variety of i-layer microstructures, from mixed-phase Si:H to highly crystalline μc-Si:H, were revealed by Raman scattering. Micro-crystallinity obtained from Raman scattering, presented as Ic/Ia, proved to be sensitive to the microstructure of μc-Si:H i-layers. Strong spatial non-uniformity of i-layer microstructure as well as variations in device performance were observed. It has been demonstrated here that stable, high performance μc-Si:H solar cells can only be obtained with i-layers being μc-Si:H, yet close to the μc-Si:H to mixed-phase Si:H transition edge where an optimum micro-crystallinity range (Ic/Ia at around 1.8) was identified. It was shown by XRD experiments that high performance, optimum μc-Si:H solar cells exhibit smaller grain sizes compared to solar cells with i-layers showing higher micro-crystallinity. Correlations among non-uniformity pattern, i-layer micro-crystallinity, and AFM surface morphologies were also observed.