Evolution of oxygenated cadmium sulfide (CdS:O) during high-temperature CdTe solar cell fabrication

Abstract

Oxygenated cadmium sulfide (CdS:O) produced by reactive sputtering has emerged as a promising alternative to conventional CdS for use as the n-type window layer in CdTe solar cells. Here, complementary techniques are used to expose the window layer (CdS or CdS:O) in completed superstrate devices and combined with a suite of materials characterization to elucidate its evolution during high temperature device processing. During device fabrication amorphous CdS:O undergoes significant interdiffusion with CdTe and recrystallization, forming CdS 1-y Te y nanocrystals whose Te fraction approaches solubility limits. Significant oxygen remains after processing, concentrated in sulfate clusters dispersed among the CdS 1-y Te y alloy phase, accounting for ~30% of the post-processed window layer based on cross-sectional microscopy. Interdiffusion and recrystallization are observed in devices with un-oxygenated CdS, but to a much lesser extent. Etching experiments suggest that the CdS thickness is minimally changed during processing, but the CdS:O window layer is reduced from 100 nm to 60-80 nm, which is confirmed by microscopy. Alloying reduces the band gap of the CdS:O window layer to 2.15 eV, but reductions in thickness and areal density improve its transmission spectrum, which is well matched to device quantum efficiency. The changes to the window layer

Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Core–Shell Nanowires

“…The high-resolution core-level XPS (HR-XPS) spectra of CdS, CdS-MHPINS, and CdS-MHP in the Cd 3d region exhibited two well-resolved peaks centered at BE ≈ 404.8 and 411.8 eV assigned to Cd 3d 5/2 and Cd 3d 3/2 peak components of Cd present in +2 oxidation state (Figure b). , The HR-XPS spectra of CdS, CdS-MHPINS, and CdS-MHP in the S 2p region were deconvoluted into three peak components located at 161.5, 162.6, and 168.6 eV (Figure c). The main intense peak at 161.5 eV originated from S 2p 3/2 while the shoulder peak at 162.6 eV was assigned to S 2p 1/2 peak components of sulfur present in the form of sulfides in CdS. , Additionally, a weak peak at 168.6 eV was assigned to sulfates (−SO 4 – ) generated due to the surface oxidation of sulfur present in CdS. , The deconvoluted HR-XPS of bulk C 3 N 5 in the C 1s region gave two peak components at 284.8 and 288.2 eV attributed to sp 3 and sp 2 hybridized carbons, respectively (Figure d) . The presence of adventitious carbons, residual unreacted precursors, and turbostratic carbons was responsible for the sp 3 (C–C) peak, while aromatic carbons (NC–N) constituting heptazine units (C 6 N 7 ) of carbon nitride framework gave rise to the sp 2 carbon peak (Figure d). , After the transformation of C 3 N 5 (MHP) bulk into monolayered sheets, the C 1s binding energies do not change, indicating that the chemical structure of C 3 N 5 remains intact during the transformation of bulk material into nanosheets under harsh acid mediated exfoliation.…”

Improving CdTe‐Based Thin‐Film Solar Cell Efficiency with the Oxygenated CdSe Layer Prepared by Sputtering Process

“…These findings are similar as the sputtered CdS:O layer which has been investigated extensively. [ 18,19 ] In the CdS:O layer, the oxygen is preferred to bond with S to formed SO 2–4 groups, [ 20 ] and the main group is SO 4 which is high resistance and wide bandgap material. [ 21 ] Meanwhile, the grain size of the CdS phase and the crystallinity of the film are decreased.…”

“…While for the high temperature annealed CdS:O film, or CdS:O after device fabrication process, its transmittance and bandgap are close to CdS film without oxygen. [ 19,23 ] During annealing process, the phase separation of CdS and CdSO 4 were observed from the transmission electron microscopy (TEM)/energy dispersive X‐ray spectroscopy (EDS) measurements, and the as‐deposited films were changed into double layer. [ 19 ] Therefore, the optical properties of the film are dominated by the CdS layer.…”

Sputtered p-Type CuxZn1–xS Back Contact to CdTe Solar Cells

“…CdTe was deposited in a closed-space sublimation (CSS) system with a source-to-substrate distance of 3 mm and source and substrate temperatures of 660 and 600 °C, respectively. After CdTe deposition, the samples were annealed in the CdCl 2 treatment at 420 °C for 10 min in a separate CSS chamber, 46 and residual CdCl 2 was rinsed off in DI water after the treatment. No other surface treatment was pursued other than water rinsing.…”