Micro-structural defects in polycrystalline silicon thin-film solar cells on glass by solid-phase crystallisation and laser-induced liquid-phase crystallisation

The microstructural properties of polycrystalline silicon films obtained by either solid-phase crystallisation (SPC) or laser-induced liquid-phase crystallisation (LPC) were investigated by transmission electron microscopy (TEM). In SPC films, the most common intra-grain defects are dislocations with the density as high as 1E10 cm−2 determined from cross-sectional weak-beam dark-field images. The highest dislocation density in LPC film is at least two orders of magnitude lower than the SPC film, 1E8 cm−2 and typically it is below 1E6 cm−2. The most common defect type in LPC films is twin boundaries and other junctions of different coincidence site lattice (CSL) boundaries. Such differences in the material structural properties result in far superior electrical performance of solar cells made of LPC films, such as mobility up to 400 cm2 V−1 s−1, similar to c-Si wafers, and the higher open-circuit voltage up to 585 mV.