Optical Losses of Frontal Layers in Superstrate CdS/CdTe Solar Cells Using OPAL2

Abstract

In this paper, optical losses in CdS/CdTe solar cells are calculated on the basis of the designated reflective index of various frontal layers using an OPAL2 calculator for the first time. Two types of glass (0.1 mm ultra-thin Schott and 1.1 mm standard borosilicate glass) were assumed to be coated by different Transparent-Conducting-Oxides (TCOs) such as SnO2:F, ZnO:Al, and ITO forming frontal layers for CdS/CdTe solar cells in superstrate configuration. Absorption, reflectance, transmittance, and consequently optical bandgap energies are calculated as a function of common thicknesses, used in the literature. The results show that an increase in TCO thickness led to a decrease in optical band gap as well as an enhancement in contact potential difference, which can deteriorate device performance. The optimum thickness of 100 nm for SnO2:F was calculated, while 200 nm for ZnO:Al and ITO show reasonable optical losses caused by reflections at the interfaces’ and the layer’s absorption. It is seen that 80 to 150 nm CdS on ITO might be an effective range to satisfy a high short circuit current and low defect densities at the CdS/CdTe interface. Finally, a minimum 2 μm thickness for the CdTe on the ultra-thin Schott glass coated by optimum layers can result in the highest short circuit current of 28.69 mA/cm2. This work offers a practical equivalent strategy to be applied for any superstrate solar cells containing TCO and CdS frontal layers.

Optical Properties Evaluation of CuIn1-xGaxSe2 Thin Films Using OPAL2 Calculator

“…There are several simulation platforms for optical analysis like MATLAB, Ray tracing [5], OPAL 2 [3] or ANSYS based on the finite element method (FEM) technique [6]. The OPAL 2 calculator is a freeware program available on the Australian PV Lighthouse website [7].…”

“…OPAL 2 calculates the transmittance, reflectance, and absorption of a thin film coating from its front surface to its substrate over a defined range of wavelengths [3,5]. The OPAL2 calculator library provides various films and substrates to model.…”

Influence of anti-reflection coatings on double GaAs/Si heterojunction layers in Si solar cells

“…Using equation ( 3), the value of the ARC layer thickness is optimized at wavelength ranges from 250 to 1200 nm, for which minimum reflectance is obtained. After obtaining the optimized thickness values of different ARCs, calculated from equation ( 3), we use the OPAL calculator [35] to calculate the different ARC layers' data. The values of the wavelengths, RIs, V OC , I SC and efficiencies are listed in table 3.…”