Oxygen Management to Avoid Photo-Inactive Cd(S,Se) for Efficient Cd(Se,Te) Solar Cells

Abstract

Our previous work has demonstrated that the formation of a penternary cadmium chalcogenide Cd­(O,S,Se,Te) region can significantly reduce the front interface recombination in Cd­(Se,Te)-based thin-film solar cells. In this work, we have shown that oxygen management during the device fabrication is crucial to form this region. While both the CdS and CdSe layer depositions and the postdeposition CdCl2 treatment should be conducted in the presence of oxygen, the CdTe deposition should be conducted in an oxygen-free atmosphere. Improper oxygen management leads to low device performance due to the formation of a photoinactive Cd­(S,Se) region and reduced absorber quality. Additionally, we investigated the carrier transport and collection properties in devices with photoinactive Cd­(S,Se) and photoactive Cd­(O,S,Se,Te) at the front interface to gain comprehensive understanding of the mechanisms that resulted in improved efficiencies approaching 20%.

Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

“…Further details can be found in our previous publications. [4,6,34] TPV/TPC Characterization: Measurements were conducted using a custom-built system, which includes a 532 nm excitation laser with a 400 ps pulse width (Market Tech, PowerChip laser PNG-M01550-130) and a high-power white LED (Thorlabs SOLIS-3C) serving as the bias light. Laser intensity was finely adjusted using continuously variable neutral density filters mounted on a translation stage, with computer-controlled adjustments to achieve the desired intensity.…”

“…We then investigate a 19.2% efficient selenized CdTe absorber‐based device. [ 4,6,34 ] We show that performing TPV and TPC measurements under different bias‐light intensities allows to determine the stationary charge carrier density and the corresponding carrier lifetimes, producing the shape predicted by Equation (). The nonradiative recombination with a lifetime of 580 ns dominates recombination at charge density below 1 × 10 14 cm −3 , and above that, the radiative recombination starts to act with a radiative recombination coefficient of 1.1 × 10 −9 cm −3 s −1 .…”

“…More information about the device performance and fabrication procedures can be found in our previous publication. [4,6,34] The device schematics and the currentvoltage characteristics under one sun illumination are given in Figure 5. TPV measurements, Figure 6a, show that an increase in bias-light intensity leads to a concurrent rise in the stationary open-circuit voltage V OC and an accelerated decay of ΔV OC (Figure 6b).…”