Thickness-Dependent Physical Properties of Coevaporated Cu 4 SnS 4 Films

Hung

Journal of Nanomaterials

et al. 2015

Cu2Sn3S7(CTS) can be used as the light absorbing layer for thin-film solar cells due to its good optical properties. In this research, the powder, baking, sulfur, and sintering (PBSS) process was used instead of vacuum sputtering or electrochemical preparation to form CTS. During sintering, Cu and Sn powders mixed in stoichiometric ratio were coated to form the thin-film precursor. It was sulfurized in a sulfur atmosphere to form CTS. The CTS film metallurgy mechanism was investigated. After sintering at 500°C, the thin film formed the Cu2Sn3S7phase and no impurity phase, improving its energy band gap. The interface of CTS film is continuous and the formation of intermetallic compound layer can increase the carrier concentration and mobility. Therefore, PBSS process prepared CTS can potentially be used as a solar cell absorption layer.

Section: Introductionmentioning

confidence: 99%

Preparation of Cu₂Sn₃S₇ Thin‐Film Using a Three‐Step Bake‐Sulfurization‐Sintering Process and Film Characterization

Hung

Journal of Nanomaterials

et al. 2015

Progress in Photovoltaics

“…Although the Raman measurements was only to a depth of approximately 100 nm by using a 514‐nm laser and the thickness of CZTSe films was approximately 1 µm, the slight intensity broad peaks at 385 and 241 cm −1 may be associated with the MoS 2 and MoSe 2 phases, respectively. Additionally, Raman shifts at the approximate positions of 312, 328, and 346 cm −1 may originate from the Cu 4 Sn(S,Se) 4 (317 cm −1 ) phase , CZTSSe phase (338 cm −1 ), and Zn(S,Se) phase (350 cm −1 ). They shift toward the low‐frequency side because of the Se incorporation.…”

Section: Resultsmentioning

confidence: 99%

High‐efficiency Cu₂ZnSn(S,Se)₄solar cells fabricated through a low‐cost solution process and a two‐step heat treatment

Chang

Chen

et al. 2016

A method for fabricating high-efficiency Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells is presented, and it is based on a nonexplosive, low-cost, and simple solution process followed by a two-step heat treatment. 2-Methoxyethanol was used as a solvent, and Cu, Zn, Sn, chloride salts, and thiourea were used as solutes. A CZTSSe absorber was prepared by sulfurising and then selenising an as-coated Cu 2 ZnSnS 4 (CZTS) film. Sulfurisation in a sulfur vapour filled furnace for a long time (2 h) enhanced the crystallisation of the as-coated CZTS film and improved the stability of the CZTS precursor, and selenisation promoted further grain growth to yield a void-free CZTSSe film. Segregation of Cu and S at the grain boundaries, the absence of a fine-grain bottom layer, and the large grain size of the CZTSSe absorber were the main factors that enhanced the grain-to-grain transport of carriers and consequently the short-circuit current (J sc ) and efficiency. The efficiency of the CZTS solar cell was 5.0%, which increased to 10.1% after selenisation. For the 10.1% CZTSSe solar cell, the external quantum efficiency was approximately 80%, the open-circuit voltage was 450 mV, the short-circuit current was 36.5 mA/cm 2 , and the fill factor was 61.9%.

“…QE maps illustrating key observations are shown in Fig. 4 influence the photocathode sensitivity [143] and that a variation in crystallite sizes can affect the energy bandgap [144]. These observations can explain the trend toward higher QE for thicker Sb films; namely, thicker films resulted in increased average crystallite and grain size, which could serve to reduce the energy band gap of the photocathodes.…”

Section: Quantum Efficiency Of Photocathodesmentioning

confidence: 86%

Thin film studies toward improving the performance of accelerator electron sources

Mamun

2016

Future electron accelerators require DC high voltage photoguns to operate beyond the present state of the art to conduct new experiments that require ultra-bright electron beams with high average current and higher bunch charge. To meet these demands, the accelerators must demonstrate improvements in a number of photogun areas including vacuum, field emission elimination in high voltage electrodes, and photocathodes. This dissertation illustrates how these improvements can be achieved by the application of suitable thin-films to the photogun structure for producing ultra-bright electron beams.This work is composed of three complementary studies. First, the outgassing rates of three nominally identical 304L stainless steel vacuum chambers were studied to determine the effects of chamber coatings (silicon and titanium nitride) and heat treatments. For an uncoated stainless steel chamber, the diffusion limited outgassing was taken over by the recombination limited process as soon as a low outgassing rate of ~1.79(0.05)  10 -13 Torr L s -1 cm -2 was achieved. An amorphous silicon coating on the stainless steel chambers exhibited recombination limited behavior and any heat treatment became ineffective in reducing the outgassing rate. A TiN coated chamber yielded the smallest apparent outgassing rate of all the chambers: 6.44(0.05)  10 -13 Torr L s -1 cm -2 following an initial 90 °C bake and 2(20)  10 -16 Torr L s -1 cm -2 following the final bake in the series. This perceived low outgassing rate was attributed to the small pumping nature of TiN coating itself.Second, the high voltage performance of three TiN-coated aluminum electrodes, before and after gas conditioning with helium, were compared to that of bare aluminum electrodes and electrodes manufactured from titanium alloy (Ti-6Al-4V). This study suggests that aluminum electrodes, coated with TiN, could simplify the task of implementing photocathode cooling, which is required for future high current electron beam applications. The best performing TiNcoated aluminum electrode demonstrated less than 15 pA of field emission current at -175 kV for a 10 mm cathode/anode gap, which corresponds to a field strength of 22.5 MV/m. Third, the effect of antimony thickness on the performance of bialkali-antimonide photocathodes was studied. The high-capacity effusion source enabled us to successfully manufacture photocathodes having a maximum QE around 10% and extended low voltage 1/e lifetime (> 90 days) at 532 nm via the co-deposition method, with relatively thick layers of antimony (≥ 300 nm). We speculate that alkali co-deposition provides optimized stoichiometry for photocathodes manufactured using thick Sb layers, which could serve as a reservoir for the alkali.In summary, this research examined the effectiveness of thin films applied on photogun chamber components to achieve an extremely high vacuum, to eliminate high voltage induced field emission from electrodes, and to generate photocurrent with high quantum yield with an extended operational lifetime. Simult...