Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices

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 studied using in situ near-infrared to ultraviolet spectroscopic ellipsometry during 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 and relative absorption strength of silicon-hydrogen infrared modes were measured by infrared extended ellipsometry measurements to gain insight into chemical bonding. Structural and optical models have been developed for the back reflector (BR) structure consisting of sputtered undoped zinc oxide (ZnO) on top of 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 were also studied by spectroscopic ellipsometry. Measurements ranging from 0.04 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 + Ag interface, and undoped a-Si:H layer in a substrate n-i-p a-Si:H based PV device structure.

Nanostructure evolution of magnetron sputtered hydrogenated silicon thin films

“…As has been observed for PECVD Si:H, 5,6,12 RF sputtered Si:H films can exhibit structural transitions at different thicknesses during deposition. In particular, we identify the thicknesses of a !…”

“…The literature describing some of these techniques, PECVD in particular, is extensive. 1,[5][6][7][8][9][10][11][12][13] In this study, we deposit thin Si:H films using RF magnetron sputtering of an undoped Si target in a mixed argon and hydrogen (Ar þ H 2 ) gas ambient atmosphere. Although existing literature describing RF-sputtered thin film Si is comparatively less comprehensive than that describing other deposition techniques, sputtering potentially offers significant advantages.…”

“…nc] structural transitions. Although these transitions occurring during PECVD of thin film Si:H are already well characterized, [5][6][7][8][9][10] RF sputtered Si:H has not received the same attention and comparatively less is known about its microstructural growth processes.…”

“…In some cases, ex-situ Raman spectroscopy may yield a significantly different result compared to XRD measurement. 18 Presently, there has been growing interest in in-situ measurement including spectroscopic ellipsometry [5][6][7][8][9][10] and Raman spectroscopy 19 to track 0021-8979/2017/122(7)/075302/8/$30.00…”

Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation

“…Real time and in-situ spectroscopic ellipsometry (SE) serve as effective tools for analysis of the optical properties of individual solar cell materials and the multilayer structures of complicated thin film devices [20,21]. For example, in a study relevant to the present research, Ranjan et al have presented the complex dielectric function (ε = ε 1 − iε 2 ) spectra of CIGS obtained by SE measurements as a function of the Cu content in the film.…”