Achieving Low V_OC-deficit Characteristics in Cu₂ZnSn(S,Se)₄ Solar Cells through Improved Carrier Separation

Abstract

Kesterite-based thin-film solar cells (TFSCs) have recently gained significant attention in the photovoltaic (PV) sector for their elemental earth abundance and low toxicity. An inclusive study from the past reveals basic knowledge about the grain boundary (GB) and grain interior (GI) interface. However, the compositional dependency of the surface potential within GBs and GIs remains unclear. The present work provides insights into the surface potential of the bulk and GB interfaces. The tin (Sn) composition is sensitive to the absorber morphology, and therefore, it significantly impacts absorber and device properties. The absorber morphology improves with the formation of larger grains as the Sn content increases. Additionally, the presence of Sn(S,Se) 2 and increased [Zn Cu + V Cu ] A-type defect cluster density are observed, validated through Raman analysis. The secondary ion mass spectroscopy analysis reveals the altered distribution of sulfur (S) and sodium (Na) with higher near-surface accumulation. The synergistic outcome of the increased density of defects and the accumulation of S near the interface provides a larger GB and GI difference and expedites carrier separation improvement. Consequently, at an optimum compositional ratio of Cu/(Zn+Sn) = ∼0.6, the power conversion efficiency (PCE) is significantly improved from 6.42 to 11.04% with a record open-circuit voltage (V OC ) deficit of 537 mV.

Back Shallow Ge Gradient Enhanced Carrier Separation for CZTSe Solar Cells through a Coselenization Process

“…Both samples show negative surface potentials, indicating that negatively charged defects dominated on the surfaces, commonly observed in CZTSSe-based materials. 32,44 Both have lower SPs at/near GBs compared with IGs, presenting that an upward band bending forms at/near GBs where holes are attracted and electrons are repelled. Thus, carrier separation occurs at/near GBs, and IGs serve as the local current paths.…”

Nanoscale Rear-Interface Passivation in Cu2ZnSn(S,Se)4 Solar Cells through the CuAlO2 Intermediate Layer

“…To study the effect of the CAO nanolayer on device performance, it was deposited on Mo-coated SLG prior to precursor (Zn/Sn/Cu) deposition. Further, the Zn/Sn/Cu stacked metallic layers were deposited at 5 °C by using a direct-current (DC) magnetron sputtering method . The detailed deposition conditions and sample names of the metallic Zn/Sn/Cu precursors are tabulated in Table .…”

“…Further, the Zn/Sn/Cu stacked metallic layers were deposited at 5 °C by using a direct-current (DC) magnetron sputtering method. 25 The detailed deposition conditions and sample names of the metallic Zn/Sn/Cu precursors are tabulated in Table 2. The deposited precursor thin films were annealed at 300 °C for 60 min in an Ar environment to form Cu−Zn and Cu−Sn alloys.…”

Understanding defects and band tailing characteristics and their impact on the device performance of Cu2ZnSn(S,Se)4 solar cells

“…Table S1† (A1–A4 samples, Zn variation) and S2 (B1–B4 samples, Cu variation) show the sample codes for CZTSSe thin films prepared with a different compositional ratio by precisely adjusting the thickness of each metallic layer in the precursors. Briefly, (i)the Cu–Sn–Zn metallic precursors were prepared on a molybdenum (Mo) back contact by the sputtering technique; 9 (ii) stacked precursors were annealed at 300 °C for 1 h under an Ar atmosphere to form Cu–Zn and Cu–Sn alloys with smooth morphology; 9,26 (iii) the soft-annealed precursors and mixed S/Se powders were placed in a graphite box in a chamber type rapid thermal annealing system and then annealed at 520 °C for 7.5 min; 9 finally (iv) the annealed thin films were naturally cooled to room temperature. The CZTSSe solar cells were fabricated with a multi-layered structure of MgF 2 /Al/Al-doped ZnO(AZO)/i-ZnO/CdS/CZTSSe/Mo/soda-lime glass (SLG).…”