Page - 63 - in Photovoltaic Materials and Electronic Devices

SpectroscopicEllipsometryStudiesofn-i-p HydrogenatedAmorphousSiliconBased PhotovoltaicDevices LaxmiKarkiGautam,MaxwellM.Junda,HamnaF.Haneef,RobertW.Collins andNikolasJ.Podraza Abstract: Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studiedusing in situnear-infraredtoultraviolet spectroscopicellipsometryduring growth of films prepared as a function of hydrogen to reactive gas flow ratio R = [H2]/[SiH4]. In conjunction with higher photon energy measurements, the presence andrelative absorption strengthof silicon-hydrogeninfraredmodes were measured by infrared extended ellipsometry measurements to gain insight into chemicalbonding. Structuraland opticalmodelshave beendeveloped for theback reflector (BR)structureconsistingofsputteredundopedzincoxide (ZnO)ontopof silver (Ag) coated glass substrates. Characterization of the free-carrier absorption properties in Ag and the ZnO + Ag interface as well as phonon modes in ZnO werealsostudiedbyspectroscopicellipsometry. Measurementsrangingfrom0.04 to 5 eV were used to extract layer thicknesses, composition, and optical response in the form of complex dielectric function spectra (ε= ε1 + iε2) for Ag, ZnO, the ZnO+Aginterface,andundopeda-Si:Hlayer inasubstraten-i-pa-Si:HbasedPV devicestructure. Reprinted from Materials. Cite as: Gautam, L.K.; Junda, M.M.; Haneef, H.F.; Collins, R.W.; Podraza, N.J. Spectroscopic Ellipsometry Studies of n-i-p HydrogenatedAmorphousSiliconBasedPhotovoltaicDevices. Materials2016, 9, 128. 1. Introduction Development of thin film technologies based on amorphous silicon and germanium, includingphotovoltaic (PV)devices, involvesunderstandingofmaterial electrical and optical properties [1–4]. It is essential to measure, monitor, and control the thickness, structure, phase, and composition of solar cell component layers in the same configuration used in manufacturing, especially for devices processed over 63