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Density of states measurements on semiconductor and thin film materials using photocurrent methods

Abstract : Investigations on thin film materials dedicated to the solar industry are still a matter of interest with the growing numbers of material types incorporated as absorbers in a solar cell device. The need of characterization techniques is therefore acute for the optimization of materials and their incorporation in solar devices. In this thesis, a photocurrent method based on Fourier Transform Photocurrent Spectroscopy (FTPS) is used to perform the measurements of thin film materials and solar cells. Our FTPS was further developed to perform 3 types of measurements: 1.) reflection and transmission (R/T) measurement, 2.) absorption coefficient spectroscopy and 3.) spectral response, external quantum efficiency, and short circuit photocurrent density measurements. This latter is specifically used for solar cells. We used the R/T results to perform numerical simulations giving the thickness, refractive index, film roughness, and optical absorption coefficient. A modeling of the density of states (DOS) using the software DeOSt automated with the Teacher Learner Based Optimization (TLBO) algorithm was achieved to find the best suited DOS parameter values to reproduce the experimental spectrum of alpha. A sensitivity analysis was performed to find the most important DOS parameters among 15-17 parameters. For the experimental studies, we have measured several a-Si:H thin film samples prepared under different deposition conditions, and used their absorption coefficient; spectra to study their DOS. A comparison of absorption coefficient; measurements on a-Si:H thin films deposited on a glass substrate and incorporated in a solar cell device stack was also conducted. This study concluded that a correction of the absorption coefficient spectrum measured on solar cells had to be done.
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Submitted on : Sunday, August 26, 2018 - 1:01:34 AM
Last modification on : Tuesday, September 29, 2020 - 4:48:53 AM
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  • HAL Id : tel-01861849, version 1

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Nastiti Puspitosari. Density of states measurements on semiconductor and thin film materials using photocurrent methods. Materials Science [cond-mat.mtrl-sci]. Université Paris Saclay (COmUE), 2018. English. ⟨NNT : 2018SACLS018⟩. ⟨tel-01861849⟩

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