This review describes recent experimental applications of small-angle X-ray (SAXS) and neutron scattering, as well as X-ray diffraction (XRD), for the determination of the microstructure of relevant solar cell thin film materials based on hydrogenated amorphous Si and SiGe alloys. Due to the recent trend toward use of amorphous Si and SiGe materials prepared near the onset of microcrystallinity, this review also describes the use of XRD to detect and determine the role of medium-range order and partial microcrystallinity in solar cell behavior. Some recent results from SAXS and XRD applied to microcrystalline Si are also summarized. (C) 2002 Elsevier Science B.V. All rights reserved.