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Environmentally friendly and earth abundant Cu2ZnSnS4 (CZTS) based thin films are potential absorbers for next generation photovoltaics. Their optical properties provide the option to be used as upper cells for Si based tandem solar cells, together with a similar structure to Si, triggering interest in investigation of CZTS/Si tandem cells. However, epitaxially growing CZTS on Si can be challenging. Here, we heteroepitaxially grow tetragonal Cu2ZnSnS4 (CZTS) thin films on single crystalline cubic Si (111) wafers with a 4° miscut by simple and low-cost radio frequency magnetron sputtering from a single target. The CZTS film displays a mirror-like surface with a surface roughness of 8.46 nm. The absorption coefficients of the epitaxial CZTS are over 104 cm−1 at 1.5 eV and 1.0 × 105 cm−1 at 2.1 eV. The bandgap is 1.45 eV, and the photoluminescence lifetime is 7.04 ns. Our results demonstrate the potential of the epitaxial CZTS films fabricated by sputtering on the Si substrate for application in CZTS/Si based tandem solar cells. [ABSTRACT FROM AUTHOR]

The earth‐abundant and environmentally‐friendly CuSbS2 solar cells have been struggling with low device performance, especially poor open circuit voltage (Voc). In this work, post‐annealing treatment of the CuSbS2/CdS heterojunction performed on CuSbS2‐based solar cells was firstly reported. With this treatment, we demonstrated CuSbS2 solar cells with a record Voc of 622 mV. The improvement of device performance was found peaked at 250°C post‐annealing which mainly benefits from the significantly boosted open‐circuit voltage and short‐circuit current. The study of microstructure by high‐resolution transmission electron microscopy revealed that such improvement could be attributed to the formation of epitaxial CuSbS2/CdS hetero‐interface upon heat treatment, which reduces the interface defect density that may lead to reduced Voc deficit. Besides, results of photoluminescence and time‐resolved photoluminescence measurements also indicated improved electrical properties of completed devices with higher photoluminescence intensity and longer minority carrier lifetime. We demonstrated significant improvement in efficiency (particularly in the Voc and Jsc) for CuSbS2 solar cells by post‐heat treatment of the CuSbS2/CdS heterojunction. The underlying correlation between post‐heat treatment and device performance reveals that the post‐heat treatment on the heterojunction leads to (1) the transformation from amorphous to epitaxial relationship of CuSbS2/CdS hetero‐interface and (2) simultaneously improved absorber quality. [ABSTRACT FROM AUTHOR]

The effects of Al layer thickness on one-step aluminium-assisted crystallization of Ge on Si have been investigated and a better understanding of the Ge growth mechanism has been obtained. The thickness of the final Ge layer is larger than the initial Al layer. The Ge growth can be divided into two stages: (i) a predominantly-vertical growth until the Ge reaches the Al surface followed by (ii) a predominantly-lateral growth with a slow vertical growth rate in order to form a continuous film. The results suggest that surplus Ge is required to obtain continuous Ge layers in one-step aluminium-assisted crystallization. [ABSTRACT FROM AUTHOR]

In this work, magnetron sputtering was used to epitaxially grow Ge films on sapphire at low temperatures (400 °C–500 °C) and diode laser annealing was employed to improve the crystallinity of the Ge films. The deposition temperature might slightly influence the crystallinity of the Ge film through affecting the diffusion rate of Ge. After laser scans of milliseconds exposure time, significant defect density reduction and removal of polycrystalline portion are achieved. Magnetron sputtering combined with diode laser annealing offers a low-cost and fast method in fabricating high quality single crystalline Ge on sapphire which is potentially capable of large-scale production. [ABSTRACT FROM AUTHOR]

In this work, epitaxial Cu2ZnSnS4 (CZTS) films grown by magnetron sputtering were annealed by continuous wavelength diode laser as an alternative post-deposition heat treatment replacing conventional post-annealing within sulfur atmosphere to improve the film quality. Upon ultrafast millisecond diode laser annealing, improvement of crystallinity and reduction of Cu/Zn disordering were observed in the CZTS thin films. The results indicate that the diode laser treatment can enable fast, effective, and efficient annealing of CZTS thin films. [ABSTRACT FROM AUTHOR]

In situ X-ray diffraction study is applied to investigate the role of annealing time in the epitaxial growth of Si x Ge 1−x on Si by aluminium-assisted crystallization at relatively low temperatures (350–450 °C). The evolution of the Si x Ge 1−x film with annealing time can be divided into two stages: (i) Si x Ge 1−x epitaxial growth on Si through Ge/Al layer exchange and (ii) Si x Ge 1-x diffusion into Si substrate. The speed of layer exchange increases with elevating temperature. After the completion of layer exchange, the Si x Ge 1−x starts diffusing into the Si substrate with prolonged annealing time. The Si content of the epitaxial Si x Ge 1−x film keeps increasing with time throughout the annealing. This increase is rapid during Ge/Al layer exchange but is gradual during Si x Ge 1−x diffusion into Si substrate. [ABSTRACT FROM AUTHOR]

Single crystalline Ge-rich Si x Ge 1-x epitaxially grown on a Si substrate is attracting great attention for its potential in optical and electronic device applications. One method of achieving Si x Ge 1-x epitaxy is by aluminium-assisted crystallization although the challenge of controlling the Si content in the Si x Ge 1-x is limited by the furnace annealing process. Herein, we report the use of a diode laser to induce aluminium-assisted crystallization of Si x Ge 1-x on Si with minimal Si content in the Si x Ge 1-x layer. By replacing furnace heat treatment with laser treatment, the reaction time is shortened from minutes to milliseconds which can limit the amount of Si incorporation into the Si x Ge 1-x films. X-ray diffraction, Raman spectroscopy, transmission electron microscopy and X-ray spectroscopy analyses are conducted on the fabricated films revealing the achievement of Ge-rich Si x Ge 1-x on Si through laser-induced aluminium-assisted crystallization. The higher laser dose may slightly increase the Si content and improve the crystallinity of the Si x Ge 1-x films. • First use of laser to induce aluminium-assisted crystallization of Si x Ge 1-x on Si • The laser-induced method reduces the reaction time from minutes to milliseconds • Achievement of Ge-rich Si x Ge 1-x on Si by this laser-induced method • Higher laser dose may improve the crystallinity of Si x Ge 1-x films [ABSTRACT FROM AUTHOR]

Sulfurization with various atmosphere and postheat treatments has been reported for earth abundant kesterite Cu2ZnSnS4 (CZTS) preparation as cost-effective material for next-generation solar cells. A full understanding of the nanoscale microstructure and chemistry of CZTS/CdS interface obtained from these different fabrication routes is currently lacking, yet is critical to developing optimal processing routes for high-performance kesterite solar cells. Here, the first detailed investigation of the interfacial microstructure and chemistry of CdS/Cu2ZnSnS4 heterojunctions is presented. For CZTS obtained from sulfurization in a sulfur-only atmosphere where highly defective surfaces are present, air annealing followed by etching in the initial stage of chemical bath deposition (CBD) process can effectively eliminate interfacial defects and allow the epitaxial growth of CBD-CdS, improving the minority lifetime, open circuit voltage ( VOC), and fill factor (FF) of the devices, while blocking Cd diffusion and deteriorating short circuit current ( Jsc). For CZTS from sulfurization in a combined sulfur and SnS atmosphere where CBD-CdS can directly epitaxially grow on CZTS and Cd-diffusion is clearly observed, associated devices show the longest lifetime and the highest efficiency of 8.76%. Epitaxial growth of CdS and Cd diffusion into CZTS are found to be two crucial features minimizing interfacial recombination and achieving high-efficiency devices. This will not only enhance the understanding of the device structure and physics of kesterite based solar cells, but also provide an effective way for designing other chalcogenide heterojunction solar cells. [ABSTRACT FROM AUTHOR]

In this work, epitaxial Ge films grown on Si by magnetron sputtering were annealed by diode laser as a replacement for conventional thermal annealing to reduce the threading dislocation density (TDD). After laser scans of millisecond exposure time, improvement of crystallinity and increase in tensile strain are observed in the Ge films. TDD of the Ge film is reduced by two orders of magnitude from 10 10 cm − 2 to 10 8 cm − 2 after only three laser scans. Diode laser annealing is a fast and low-cost method to effectively reduce TDD in epitaxial Ge films on Si. [ABSTRACT FROM AUTHOR]

In this work, epitaxial growth of Ge on Si is achieved using magnetron sputtering which is a low-cost and safe method suitable for large-scale production. Smooth surface with RMS roughness of 0.48 nm is obtained at a low deposition temperature of 300 °C. Cyclic thermal annealing is applied to the Ge film reducing the threading dislocation density (TDD) by two orders of magnitude. The in-plane strain in the Ge film changes from compressive to tensile after annealing due to the mismatch in thermal expansion coefficients between Si and Ge. The mechanism of the TDD reduction is investigated revealing formation of dislocation loops and dissociation of dislocations into planar defects at the interface. The Ge epitaxy film on Si may be suitable for use as virtual substrate for the fabrication of III–V high efficiency solar cells. [ABSTRACT FROM AUTHOR]

Aluminium-assisted crystallization is used to grow single-crystalline SixGe1−x film epitaxially on Si substrate at a relatively low temperature (350–450°C). Investigation of the mechanism by which Al film causes epitaxial growth of SixGe1−x suggests a four-step growth process is involved. The composition of the SixGe1−x film can be controlled by the annealing conditions. This SixGe1−x film can be used as a buffer layer for the epitaxial growth of Ge on Si or as a virtual substrate for the fabrication of III–V devices. [ABSTRACT FROM AUTHOR]