Through-the-glass spectroscopic ellipsometry for analysis of CdTe thin-film solar cells in the superstrate configuration

Koirala, Prakash; Li, Jian; Yoon, Heayoung P.; Aryal, Puruswottam; Marsillac, Sylvain; Rockett, Angus; Podraza, Nikolas J.; Collins, R. W.

doi:10.1002/pip.2759

Cited by 54 publications

(28 citation statements)

References 26 publications

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“…These window layer effects correct the offset in the ellipsometric angle Δ , arising from any stress‐induced birefringence in the Si wafer along the path of the incident beam of light. Similar issues are encountered in the through‐the‐glass measurement configuration applied for characterization of other materials such as CdTe PV in the superstrate configuration . As the beam of light only travels through air before reaching the optically opaque Al layer in the film side measurement configuration, window effects and reflection corrections are not necessary in that case.…”

Section: Resultsmentioning

confidence: 99%

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

Subedi

Silverman

Deceglie

et al. 2017

Physica Status Solidi (a)

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Al is a commonly used material for rear side metallization in commercial silicon (Si) wafer solar cells. In this study, through‐the‐silicon spectroscopic ellipsometry is used in a test sample to measure Al+Si interface optical properties like those in Si wafer solar cells. Two different spectroscopic ellipsometers are used for measurement of Al+Si interface optical properties over the 1128–2500 nm wavelength range. For validation, the measured interface optical properties are used in a ray tracing simulation over the 300–2500 nm wavelength range for an encapsulated Si solar cell having random pyramidal texture. The ray tracing model matches well with the measured total reflectance at normal incidence of a commercially available Si module. The Al+Si optical properties presented here enable quantitative assessment of major irradiance/current flux losses arising from reflection and parasitic absorption in encapsulated Si solar cells.

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Section: Resultsmentioning

confidence: 99%

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

Subedi

Silverman

Deceglie

et al. 2017

Physica Status Solidi (a)

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“…The ray tracing method is utilized to compute the paths of the scattered light until becoming fully extinct. The optical coefficients (n and k) of C 1−x Z x T [12], Mg x Zn 1−x O (MZO) [13], Cd x Zn 1−x O (CZO) [14], cadmium sulfide (CdS) [15], ethylene/vinyl acetate (EVA) [16], silicon [17], glass [18], and indium-tin-oxide (ITO) [19] used in our calculations are taken from the literature. The refractive index spectra of molybdenum oxide (MoO x ) and magnesium fluoride (MgF 2 ) are obtained via spectroscopic ellipsometry measurements (SOPRA GES-5E) with a spectral range from 1.23 to 5 eV using thermally evaporated layers on a c-Si substrate at 70 • incidence angle.…”

Section: Methodsmentioning

confidence: 99%

Combined Optical-Electrical Optimization of Cd1−xZnxTe/Silicon Tandem Solar Cells

2020

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Although the fundamental limits have been established for the single junction solar cells, tandem configurations are one of the promising approaches to surpass these limits. One of the candidates for the top cell absorber is CdTe, as the CdTe photovoltaic technology has significant advantages: stability, high performance, and relatively inexpensive. In addition, it is possible to tune the CdTe bandgap by introducing, for example, Zn into the composition, forming Cd1−xZnxTe alloys, which can fulfill the Shockley–Queisser limit design criteria for tandem devices. The interdigitated back contact (IBC) silicon solar cells presented record high efficiencies recently, making them an attractive candidate for the rear cell. In this work, we present a combined optical and electrical optimization of Cd1−xZnxTe/IBC Si tandem configurations. Optical and electrical loss mechanisms are addressed, and individual layers are optimized. Alternative electron transport layers and transparent conductive electrodes are discussed for maximizing the top cell and tandem efficiency.

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“…Thus, setting up an accurate and relevant complex dielectric function database for devices can entail considerable background work. Confidence in the relevance and validity of the database can be obtained through studies that apply SE-deduced optical models to analyze complete solar cell structures and predict solar cell performance [19][20][21][22] .…”

Section: Methodsmentioning

confidence: 99%

“…The EQE simulations described here, based on the SE analysis of standard high-performance CIGS solar cells, apply the assumption that all carriers photo-generated within the active layers of the cell are collected without recombination losses. Any differences between the simulated EQE obtained using input parameters from SE analysis and the experimental EQE from the measurement of a completed solar cell can provide information on possible breakdowns of the assumptions applied in the simulations, as has been described in studies of different thin film PV technologies [10,[18][19][20] . Specifically, lower measured EQE values compared with the simulation can be attributed to losses due to recombi-nation of carriers generated by photons absorbed within the active layers.…”

Section: Introductionmentioning

confidence: 99%

Optical simulation of external quantum efficiency spectra of CuIn1−Ga Se2 solar cells from spectroscopic ellipsometry inputs

Ibdah

Koirala

Aryal

et al. 2018

Journal of Energy Chemistry

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Applications of in-situ and ex-situ spectroscopic ellipsometry (SE) are presented for the development of parametric expressions that define the real and imaginary parts (ε 1 , ε 2) of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency (EQE) without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics (PV) technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide (CuIn 1 −x Ga x Se 2 ; CIGS) solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness (> 2 μm) and thin (< 1 μm) absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate (ε 1 , ε 2) database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a ∼0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of < 1 s per (ψ,) spectra achievable by the multichannel ellipsometer.

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Through-the-glass spectroscopic ellipsometry for analysis of CdTe thin-film solar cells in the superstrate configuration

Cited by 54 publications

References 26 publications

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

Combined Optical-Electrical Optimization of Cd1−xZnxTe/Silicon Tandem Solar Cells

Optical simulation of external quantum efficiency spectra of CuIn1−Ga Se2 solar cells from spectroscopic ellipsometry inputs

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