Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cells on ZnO:Al

Abstract

The combination of polycrystalline silicon (poly-Si) thin films with aluminum doped zinc oxide layers (ZnO:Al) as transparent conductive oxide enables the design of appealing optoelectronic devices at low costs, namely in the field of photovoltaics. The fabrication of both thin-film materials requires high-temperature treatments, which are highly desired for obtaining a high electrical material quality. Annealing procedures are typically applied during crystallization and defect-healing processes for silicon and can boost the carrier mobility and conductivity of ZnO:Al layers. In a combined poly-Si/ZnO:Al layer system, an in-depth knowledge of the interaction of both layers and the control of interface reactions upon thermal treatments is crucial. Therefore, we analyze the influence of rapid thermal treatments up to 1050 °C on solid phase crystallized poly-Si thin-film solar cells on ZnO:Al-coated glass, focusing on chemical interface reactions and modifications of the poly-Si absorber material quality. The presence of a ZnO:Al layer in the solar cell stack was found to limit the poly-Si solar cell performance with open circuit voltages only below 390 mV (compared to 435 mV without ZnO film), even if a silicon nitride (SiN) diffusion barrier was included. A considerable amount of diffused zinc inside the silicon was observed. By grazing-incidence X-ray fluorescence spectrometry, a depth-resolving analysis of the elemental composition close to the poly-Si/(SiN)/ZnO:Al interface was carried out. Temperatures above 1000 °C were found to promote the formation of new chemical compounds within about 10 nm of interface, such as zinc silicates (Zn2SiO4) and aluminium oxide (AlxOy). These results give valuable insights about the temperature-limitations of Si/ZnO thin-film solar cell fabrication and the formation of high-mobility ZnO-layers by thermal anneal.

Atomic-layer-deposited Al-doped zinc oxide as a passivating conductive contacting layer for n+-doped surfaces in silicon solar cells

“…Moreover, if effusion of hydrogen from the stack was the main cause for the loss of passivation, the different onset temperatures at which the passivation starts to decrease that is observed for the different interfacial oxides would not be expected, provided the passivation level of the various oxides reacts similarly to dehydrogenation. Finally, it has been shown in studies on poly-Si(n)/ZnO:Al structures that ZnO can reduce to metallic Zn at temperatures exceeding 600 o C, especially in the presence of hydrogen, and that this Zn can moreover diffuse into the silicon forming recombination centers [59,60]. Although the loss of passivation in this work is observed at somewhat lower temperatures, such a mechanism cannot be excluded.…”

Carbon nanotube modified Zn 0.83 Cd 0.17 S nanocomposite photocatalyst and its hydrogen production under visible-light

“…The spectra shows the most intense characteristic Raman bands at 328.4 cm À1 and a less intense characteristic Raman bands at 556.1 cm À1 , which can be assigned to the 1st longitudinal-optical phonon (1 LO) and 2nd longitudinal-optical phonon (2 LO), respectively. The peaks of CdS Raman characteristic are reported to be at 296 and 596 cm À1 and those of ZnS at 298 and 604 cm À1 [27]. The difference between the samples and pure CdS and ZnS indicates that the sulfide solid solution is formed instead of the mixture of CdS and ZnS, which can further verified by the XRD pattern in Fig.…”

“…The surface-treatment method of CNTs can be found in Ref. [27]. Then the mixed solution was purged in the 50 ml-Teflon-lined container, and followed by Ar purification for 10 min.…”

Grazing incidence X-ray fluorescence analysis of buried interfaces in periodically structured crystalline silicon thin-film solar cells

“…X‐ray fluorescence (XRF) techniques combined with a completely reference‐free fundamental parameter approach have proven to be useful tools for the characterization of nano‐layered samples , depth profiling , and interface characteristics in chalcopyrite solar cells, as well as chemical speciation at buried interfaces in silicon thin‐film solar cells on ZnO:Al . Yet, only few studies have been conducted on sample systems featuring 3D structures, e.g., the depth‐profiling of vertical sidewall nanolayers on structured wafers .…”