F. Haque

Prospects of Zinc Sulphide as an alternative buffer layer for CZTS solar cells from numerical analysis

Zinc Sulphide (ZnS) is a promising candidate to be an alternative buffer layer to the commonly used cadmium sulphide (CdS) in CZTS solar cells. In this study, buffer layer parameters like layer thickness and buffer layer bandgap have been investigated by Analysis of Microelectronic and Photonic Structures (AMPS-1D) to find out the higher conversion efficiency. A promising result has been achieved with an efficiency of 14.49% (with Voc = 0.81 V, Jsc = 28.85 mA/cm2 and Fill factor = 67.5) by using ZnS as a buffer layer. It is also found that the high efficiency of CZTS absorber layer thickness is between 2 μm and 4 μm. From the simulation results, it is revealed that higher efficiency can be achieved for the buffer layer bandgap around 3.10 eV - 3.25 eV. This result can be explained by the practical work as the bandgap of ZnS is largely dependent on the preparation conditions and stoichiometry. In conclusion, numerous influences of buffer layer are investigated in CZTS solar cell that can lead to the fabrication of high efficiency devices.

Design optimization of CdTe thin film solar cells from numerical analysis

In this paper, a modified structure for CdTe thin film solar cell was proposed by numerical analysis with an addition of a novel ZnO buffer to improve the conversion efficiency. The CdS window layer was reduced to 50 nm together with the insertion of zinc oxide (ZnO) as the buffer layer to prevent forward leakage current. The thickness of CdTe absorber layer was varied from 1000 nm to 5000 nm and as well as the operating temperature was also varied from 25°C to 165°C. The numerical simulation was done by Analysis of Microelectronic and Photonic Structures (AMPS-1D) simulator. The highest conversion efficiency obtained was 20.27% (Voc = 1.08 V, Jsc = 24.93 mA/cm2, FF = 0.83) with 5000 nm CdTe absorber layer and 50 nm CdS window layer. Moreover it was observed that with the increase in operating temperature, the normalized efficiency decreased linearly at a gradient of 0.2%/°C, which reveals that the CdTe thin film solar cell has higher stability.

Influence of thermal annealing on CdTe thin film deposited by thermal evaporation technique

Effects of thermal annealing on the structural and optical properties of thermally evaporated CdTe thin films are presented here. Thin films of CdTe were deposited on soda lime glass substrates at room temperature by varying the deposition current ranging from 25 Amperes to 30 Amperes by thermal evaporation. The grown samples were annealed at the annealing temperature of 400°C for 15 minutes in a vacuum furnace of nitrogen ambient with pressure of 250–300 mTorr. The structural, optical and electrical properties of the grown samples were investigated by XRD, AFM and UV-VIS spectrometry. The as-deposited films prepared at deposition current 25A shows polycrystalline nature whereas the films prepared at 28A and 30A exhibit cubic crystallinity with (111) preferential orientation around 2θ=23.8°. The surface roughness of the films is also highly affected by the thermal annealing as observed from the AFM images. The band gap has been found around 1.5 eV for the as-deposited film whereas the band gap decreased approximately to 1.4 eV after thermal annealing treatment.

Nanostructured and wide bandgap CdS:O thin films grown by reactive RF sputtering

In this study, CdS:O thin films were prepared from a 99.999% CdS target by reactive sputtering in a Ar:O2 (99:1) ambient with different RF power at room temperature. The deposited films were studied by means of XRD, SEM, EDX, Hall Effect and UV-Vis spectrometry. The incorporations of O2 into the films were observed to increase with the decrease of deposition power. The cryatallinity of the films were reduced, whereas the band gaps of the films were increased by the increase of O2 content on the films. The films were found in nano-structured grains with a compact surface. It has been seen that the highest carrier density is observed in the film with O2 at.% 21.10, while the values decreased with the further increase or decrease of O2 content on the films; indicating that specific amount of donor like O2 atoms substitute to the S atoms can improve the carrier density of the CdS:O thin film.