Interface Analysis of Cu(In,Ga)Se2 and ZnS Formed Using Sulfur Thermal Cracker

Abstract

We analyzed the interface characteristics of Zn‐based thin‐film buffer layers formed by a sulfur thermal cracker on a Cu(In,Ga)Se2 (CIGS) light‐absorber layer. The analyzed Zn‐based thin‐film buffer layers are processed by a proposed method comprising two processes — Zn‐sputtering and cracker‐sulfurization. The processed buffer layers are then suitable to be used in the fabrication of highly efficient CIGS solar cells. Among the various Zn‐based film thicknesses, an 8 nm–thick Zn‐based film shows the highest power conversion efficiency for a solar cell. The band alignment of the buffer/CIGS was investigated by measuring the band‐gap energies and valence band levels across the depth direction. The conduction band difference between the near surface and interface in the buffer layer enables an efficient electron transport across the junction. We found the origin of the energy band structure by observing the chemical states. The fabricated buffer/CIGS layers have a structurally and chemically distinct interface with little elemental inter‐diffusion.

Electrodeposition Fabrication of Chalcogenide Thin Films for Photovoltaic Applications

“…ZnS is an inexpensive semiconductor with an energy band gap of 3.72 eV in the cubic phase and 3.77 eV in the hexagonal wurtzite phase. In thin film photovoltaic devices, ZnS has been majorly employed as an n-type material to form a p-n junction by pairing with a p-type material, for example, Cu(In,Ga)Se 2 (CIGSe) [80] or Cu 2 ZnSnS 4 (CZTS) [81,82]. ZnS can be electrochemically deposited with either an alkaline electrolyte or an acidic electrolyte.…”

Complementary hybrid electrodes for high contrast electrochromic devices with fast response

“…So far, ATO NPLs were used solely as a passive ion-storage layer 29 . The preparation of the ATO NPL (particle diameter: 13–22 nm) was performed by using a commercially available ATO nanopowder following the process developed by Cho et al 30 .…”

Ultrafast Photocarrier Dynamics at the p–n Junction in Cu(In,Ga)Se2 Solar Cell with Various Zn(O,S) Buffer Layers Measured by Optical Pump–Terahertz Probe Spectroscopy

“…We prepared the three types of Zn­(O,S) buffer layers, cracker-Zn­(O,S), CBD-Zn­(O,S), and sputter-Zn­(O,S), based on reference recipes in our laboratory. The cracker-Zn­(O,S) buffer layer was prepared by a two-step process: a Zn film of 3 nm was first deposited on the CIGS layer by the sputtering method with working pressure of 40 W at room temperature and then sulfurized using the S thermal cracker chamber at a substrate temperature of 550 °C for 10 min, resulting in a cracker-Zn­(O,S) film of 8 nm. , A CBD-Zn­(O,S) buffer layer with a thickness of ∼30 nm was synthesized in an aqueous solution by precipitating the ZnS phase at 85 °C in a homemade water bath system under fixed deposition conditions: a zinc sulfate mole concentration of 0.02 M, thiourea of 0.08 M, and ammonia concentration of 2 M for 45 min. , The 70 nm thick Zn­(O,S) layer was deposited by RF sputtering: a ZnS target (4 in.) at RF power of 150 W and a mixture gas (90/10 Ar/O 2 (%)) were introduced simultaneously at a steady total gas flow rate of 100 cm 3 (STP) min –1 at a substrate temperature of 200 °C. , Since we wanted to ensure well-made layers for each Zn­(O,S) buffer type in the completed CIGS solar cell, their thicknesses were different.…”

“…In this study, we fabricated CIGS solar cells with three types of Zn­(O,S) buffer layer, grown by different techniques based on previous results in our laboratory, specifically, the S thermal cracking (cracker), , chemical bath deposition (CBD), , and reactive sputtering (sputter) , methods. Since optically excited carriers (“photocarriers”) can determine the cell’s photovoltaic performance, depending on whether the photocarriers are trapped at defect states or not, it is crucially important to examine photocarrier dynamics.…”