Conductivity mechanisms and influence of the Cu/Zn disorder on electronic properties of the powder Cu2ZnSn(S1-xSex)4 solid solutions (original) (raw)
Related papers
Journal of Alloys and Compounds, 2015
This work studied the electrical effects of the substitution of tin with silicon on p-type Cu 2 ZnSnS 4 semiconductor compounds. To this purpose, two samples, namely Cu 2 ZnSnS 4 and Cu 2 ZnSn 0.5 Si 0.5 S 4 , were prepared. The samples purities and homogeneities were characterized by both Energy Dispersive X-ray (EDX) spectroscopy and powder X-ray diffraction (PXRD). We observed that the temperature dependence of the electrical conductivity of materials exhibits a crossover from T À1/4 to T À1 dependence in the temperature range between 130 and 140 K. The characteristic temperature (T 0,Mott), the hopping distance (R hop), the average hopping energy (D hop), the localization length (n) and the density of states (N(E F)), were determined, and their values were discussed within the models describing conductivity in p-type semiconductor.
Effects of the Cu variation in Cu 2Àx Zn 0.9 Sn 1.1 Se 4 (Sn-rich CZTSe) bulks with x = 0-0.3 on the morphological, structural, and electrical properties have been investigated. Conventionally, the rich in Sn is prohibited for CZTSe because of the formation of the n-type and low electrical mobility. Cu 2Àx (Zn 0.9 Sn 1.1)Se 4 pellets show as the p-type at x = 0 and 0.1 and the n-type at x = 0.2 and 0.3. Sn-rich CZTSe at x = 0 and 0.1 has high mobilities of 87.1 and 58.4 cm 2 /V s and favorable hole concentrations of 7.52 Â 10 17 and 4.88 Â 10 17 cm À3 , respectively. SEM surface images have shown that the grains are less densely packed as the copper content decreases. The non-stoichiometric composition of Sn-rich CZTSe under various Cu contents can lead to the intrinsic defects, with which the changes in the structural and electrical properties of the bulks with the Cu ratio can be explained. This work provides the promising results for Sn-rich CZTSe with the Sn excess to control the hole concentration and the Cu content to keep high electrical mobility.
Journal of Alloys and Compounds, 2013
Cu-deficient Cu 2 ZnSn(S x Se 1Àx) 4 (CZTSSe) pellets were fabricated by reactive liquid-phase sintering at 600°C with two types of sintering aids of Sb 2 S 3 and Te and two types of compensation discs of CuSe 2 and SnSe 2 for selenization and CuS and SnSe 2 for sulfo-selenization and sulfurization. Selenides of Cu 2 Se, ZnSe, SnSe 2 , and SnSe and sulfides of CuS, ZnS, and SnS were the constituent powders. Comprehensive characterizations of the CZTSSe pellets at different S/(S + Se) ratios were performed. The compositions of Cu, Zn, Sn, and the sum of all anionic elements did not change with the sulfur content. No second phases were detected. The highest mobility of 3.5 cm 2 V À1 s À1 was obtained for CZTSSe at x = 0.5. Electrical property of polycrystalline CZTSSe is important for making thin-film solar cells, but systematic investigation was limited. We systematically measured the electrical property of CZTSSe bulks and found that carrier mobility was an important factor in selecting the absorber materials.
Electrical properties and electronic structure of Cu1−xZnxInSe2 and Cu1−xZnxInS2 single crystals
Journal of Physics and Chemistry of Solids, 2015
Temperature dependence of the electrical conductivity of CuInS 2 -ZnIn 2 S 4 and CuInSe 2 -ZnIn 2 Se 4 solid solutions possessing n-type conductivity has been studied. It has been established that when the temperature decreases down to $ 100 to 27 K, the hopping mechanism of electrical conductivity with a variable jumping length between localized states positioned in a narrow energy band near the Fermi level becomes dominant. The main parameters of the hopping conductivity have been determined. At higher temperatures (150-300 K), in the CuInSe 2 -ZnIn 2 Se 4 single crystals containing 15 and 20 mol% ZnIn 2 Se 4 the thermally activated conductivity with activation energy of 0.018 and 0.04 eV, respectively, is detected. Among the CuInSe 2 -ZnIn 2 Se 4 single crystals, samples with 5 and 10 mol% ZnIn 2 Se 4 were found to be close to degenerate semiconductors. Temperature dependences of the electrical conductivity of CuInS 2 -ZnIn 2 S 4 single crystals are described by a more complicated function that may indicate a competition of several conduction mechanisms in these compounds. For the CuInS 2 -ZnIn 2 S 4 solid solutions, X-ray photoelectron core-level and valence-band spectra have been measured for both pristine and Ar þ ion-bombarded surfaces. Our results indicate that the Cu 1 À x Zn x InS 2 single-crystal surfaces are sensitive to Ar þ ion-bombardment. Additionally, for the Cu 1 À x Zn x InS 2 crystal with the highest ZnIn 2 S 4 content, namely 12 mol% ZnIn 2 S 4 , the X-ray emission bands representing the energy distribution of the Cu 3d, Zn 3d and S 3p states have been measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum.
Optical Materials, 2012
Single crystals of Cu 2 ZnSn(S x Se 1Àx ) 4 (CZTSSe) solid solutions were grown by chemical vapor transport technique using iodine trichloride as a transport agent. As confirmed by X-ray investigations, the as-grown CZTSSe solid solutions are single phase and crystallized in kesterite structure. The lattice parameters of CZTSSe were determined and the S contents of the obtained crystals were estimated by Vegard's law. The composition dependent band gaps of CZTSSe solid solutions were studied by electrolyte electroreflectance (EER) measurements at room temperature. From a detailed lineshape fit of the EER spectra, the band gaps of CZTSSe were determined accurately and were found to decrease almost linearly with the increase of Se content, which agreed well with the recent theoretical first-principle calculations by
Vibrational and structural properties of Cu2ZnSn(SxSe1−x)4 (0 ≤ x ≤ 1) solid solutions
2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014
As the interest in CU2ZnSn(S,Sel_,)4 (0 :s x :s 1) kesterite based thin film solar cells increases, the development of new processes and characterization methodologies are required to satisfy its own peculiarities. In order to achieve better device performance and higher efficiencies a detailed systematic study of the fundamental properties of these materials is required. In this study, Raman spectroscopy and X-ray diffraction (XRD) were applied together to evaluate the crystal structure and the phonon modes of the CU2ZnSn(S,Sel_,)4 solid solutions leading to the complete characterization of the structural and vibrational properties.
Composition Dependent Band Gaps of Single Crystal Cu2ZnSn (SxSe1-x) 4 Solid Solutions
Solid State Phenomena, 2013
Single crystals of Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) solid solutions have deen grown by chemical vapor transport technique using ICl 3 as a transport agent. Analyzing the X-ray diffraction patterns reveal that the as-grown CZTSSe solid solutions are crystallized in kesterite structure and the lattice parameters are determined. The S contents of the obtained crystals are estimated by Vegard's law. The composition dependent band gaps of CZTSSe solid solutions are studied by electrolyte electroreflectance (EER) techniques. The band gaps of CZTSSe are evaluated by a lineshape fit of the EER spectra and are found to increase almost linearly with the increase of S content.
Understanding the relationship between Cu2ZnSn(S,Se)4 material properties and device performance
MRS Communications, 2014
Cu 2 ZnSn(S,Se) 4 (CZTSSe) photovoltaics (PV) have long been considered promising candidates for large-scale PV deployment due to the availability of constituent elements and steady improvements in device efficiency over time. The key limitation to high efficiency in this technology remains a deficit in the open-circuit voltage with respect to the band gap. The past decade has seen significant progress toward understanding how the various material properties such as bulk and surface composition, point defects (intrinsic and extrinsic), and grain boundaries all impact the optoelectronic properties of CZTSSe materials, and consequently device performance. This paper aims to summarize what is known about the CZTSSe bulk and surfaces, and how these material properties may be related to the Voc deficit.
Applied Physics Express, 2012
The concept of defect chemistry is applied to investigate the defects in Cu-deficient Cu 2 ZnSnSe 4 (CZTSe) bulks liquid-phase sintered at 600 C with soluble sintering aids of Sb 2 S 3 and Te. By changing the Zn/Sn ratio, CZTSe changed from n-type to p-type semiconductor. Measurements of electrical properties with the changes in the Zn/Sn ratio were carried out to determine defect behaviors. Current jump in current-voltage tests and the big change in mobility can be attributed to the existence of Cu 2þ defects, which became dominant at a higher Zn/Sn ratio of 1.35 and introduced stronger plasmon interaction. # 2012 The Japan Society of Applied Physics T he recent breakthroughs in Cu-deficient Cu 2 ZnSnSe 4 (CZTSe) thin-film solar cells with efficiencies of 10.1% by a nonvacuum process and 9.15% by a coevaporation process have made it a candidate for future application, which was also based on its low costs of earthabundant constituents and thin-film form. 1,2) As compared with Cu 2 (In,Ga) 2 Se 4 (CIGSe), however, CZTSe was attracted fewer interest and investigations. More research works can allow it to compete with CIGSe. Studies on defects of I-III-VI-type semiconductors have been focused on the device performance in order to enhance solar cell efficiency by maximizing the open-circuit voltage and short-circuit current. Conventional defect studies in bulk form are rare because the bulk materials of these I-III-VItype semiconductors are difficult to synthesize by sintering due to Se vaporization. That is the reason why the reported semiconductors have been grown as crystals in a sealed quartz tube. 3-6) Our studies on defects of sintered CZTSe bulk and its effects on electrical property require having sintered dense specimens. To enhance sintering at low temperature, sintering aids should be added to assist the densification by liquid-phase sintering. In this study, reactive sintering should have sintering aids dissolved into CZTSe to form a solid solution. With this easily assessable powder metallurgy approach, we can systematically adjust the composition in order to investigate its effects on property. CZTSe is an ionic solid and its defect formation should maintain charge, lattice site, and mass balances. The Kröger-Vink notation developed to describe the defects in an ionic compound will be applied here. 7) For the Cudeficient and p-type CZTSe as an example, the formation of each Cu þ vacancy with a relative charge of À1 or V Cu 0 as an acceptor is associated with a hole, h. V Cu , Cu Zn , and Zn Cu defects have been mentioned. 8-10) Here, we investigate Cu-deficient CZTSe bulks with different Zn/Sn ratios. The variations of microstructure and electrical property with the Zn/Sn ratio or defect behavior are investigated. The Cu-deficient CZTSe bulks, which are expressed using the formula Cu 1:6 (Zn 1þx Sn 1Àx)Se 4 , were prepared by liquidphase sintering at 600 C for 1 h with sintering aids of Sb 2 S 3 and Te. The constituent weights were actually based on the actual formula of Cu 1:6 [(Zn 1þx Sn 1Àx) 0:9 Sb 0:2 ](Se 3:3 S 0:3 Te 0:4).