  A light source of selective functionalities of wavelengths, illumination
periods, and intensities is desirable for investigating performance parameters
as well as the quality of different layers and interfaces of solar cells.
Conventional light sources used for these types of research are expensive,
space-consuming, cumbersome to work with, and have limited functionalities. We
have developed a light source with variable wavelength, intensity, and
illumination period to address these issues using an illumination period
control unit, voltage regulator, neutral density filter, alterable light
emitting diodes, etc. As a proof-of-concept, we employed our constructed light
source to investigate the intensity, wavelength, illumination period modulated
photovoltaic, and impedance properties of inorganic thin film solar cells such
as cadmium telluride (CdTe) and copper zinc tin sulfide (CZTS) using lights of
wavelength 410, 520, and 635 nm. We hope to use this light source for
photophysical and photochemical studies of metal oxide materials used for
renewable energy research.
