다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The path towards a high-performance solution-processed kesterite solar cell ☆

The kesterite-structured semiconductors Cu2ZnSnS4 and Cu2ZnSnSe4 are drawing considerable attention recently as the active layers in earth-abundant low-cost thin-film solar cells. The additional number of elements in these quaternary compounds, relative to binary and ternary semiconductors, results in increased flexibility in the material properties. Conversely, a large variety of intrinsic lattice defects can also be formed, which have important influence on their optical and electrical properties, and hence their photovoltaic performance. Experimental identification of these defects is currently limited due to poor sample quality. Here recent theoretical research on defect formation and ionization in kesterite materials is reviewed based on new systematic calculations, and compared with the better studied chalcopyrite materials CuGaSe2 and CuInSe2 . Four features are revealed and highlighted: (i) the strong phase-competition between the kesterites and the coexisting secondary compounds; (ii) the intrinsic p-type conductivity determined by the high population of acceptor CuZn antisites and Cu vacancies, and their dependence on the Cu/(Zn+Sn) and Zn/Sn ratio; (iii) the role of charge-compensated defect clusters such as [2CuZn +SnZn ], [VCu +ZnCu ] and [ZnSn +2ZnCu ] and their contribution to non-stoichiometry; (iv) the electron-trapping effect of the abundant [2CuZn +SnZn ] clusters, especially in Cu2ZnSnS4. The calculated properties explain the experimental observation that Cu poor and Zn rich conditions (Cu/(Zn+Sn) ≈ 0.8 and Zn/Sn ≈ 1.2) result in the highest solar cell efficiency, as well as suggesting an efficiency limitation in Cu2ZnSn(S,Se)4 cells when the S composition is high.

Classification of lattice defects in the kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 earth-abundant solar cell absorbers.

(AgIn)xZn2(1-x)S2 solid solutions between ZnS photocatalyst with a wide band gap and AgInS2 with a narrow band gap showed photocatalytic activities for H2 evolution from aqueous solutions containing sacrificial reagents, SO32- and S2-, under visible-light irradiation (λ ≥ 420 nm) even without Pt cocatalysts. Loading of the Pt cocatalysts improved the photocatalytic activity. Pt (3 wt %)-loaded (AgIn)0.22Zn1.56S2 with a 2.3 eV band gap showed the highest activity for H2 evolution, and the apparent quantum yield at 420 nm amounted to 20%. H2 gas evolved at a rate of 3.3 L m-2·h-1 under irradiation using a solar simulator (AM 1.5). The diffuse reflection and the photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side as the ratio of AgInS2 to ZnS increased in the solid solutions. The photocatalytic H2 evolution depended on the compositions as well as the photophysical properties. The dependence of the photophysical and photocatalytic properties upon the composition wa...

Photocatalytic H2 evolution reaction from aqueous solutions over band structure-controlled (AgIn)xZn2(1-x)S2 solid solution photocatalysts with visible-light response and their surface nanostructures.

ZnO nanorod arrays were fabricated using a hydrothermal method. The nanorods were studied by scanning electron microscopy, photoluminescence (PL), time-resolved PL, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy before and after annealing in different environments and at different temperatures. Annealing atmosphere and temperature had significant effects on the PL spectrum, while in all cases the positron diffusion length and PL decay times were increased. We found that, while the defect emission can be significantly reduced by annealing at 200 °C, the rods still have large defect concentrations as confirmed by their low positron diffusion length and short PL decay time constants.

Defects in ZnO nanorods prepared by a hydrothermal method

Cu 2 Zn 1-x Cd x Sn(Se 1-y S y ) 4 monograin powders with different x- and y-values were prepared from binary compounds in the liquid phase of flux material (KI) in evacuated quartz ampoules. All the materials had uniform composition and p-type conductivity. PL spectra (10 K) of the as grown Cu 2 Zn 1-x Cd x Sn(Se) 4 monograin powders showed one PL band with peak position around 0.85 eV which shifted linearly to the lower energy side with increasing Cd content. Cu 2 ZnSnS 4 material showed asymmetrical PL band at 1.31 eV attributed to band-to-tail recombination. RT Raman spectra of Cu 2 ZnSnSe 4 revealed two main peaks at 196 cm -1 and 173 cm -1 and a third less intensive peak with varying peak position in the region 231-253 cm -1 . Raman spectra of Cu 2 ZnSnS 4 showed an intensive peak at 338 cm -1 and additional peaks at 287 cm -1 and 368 cm -1 . Narrow sieved fractions of grown powders were used as absorber materials in monograin layer (MGL) solar cell structures: graphite/ Cu 2 Zn 1-x Cd x Sn(Se 1-y S y ) 4 /CdS/ZnO. The best so far solar cell that was based on the Cu 2 Zn 0.8 Cd 0.2 SnSe 4 had open circuit voltage 422 mV, short circuit current 12 mA/cm 2 and fill fac tor 44%.

Cu2Zn1–xCdx Sn(Se1–ySy)4 solid solutions as absorber materials for solar cells

http://staff.ttu.ee/~krustok/PDF-s/Maarja%202011%20TSF.pdf

Photoluminescence and Raman study of Cu2ZnSn(SexS1 − x)4 monograins for photovoltaic applications

Several experimental photoluminescence (PL) bands of different energies for variously prepared CdTe samples are compared. Temperature variation of the PL intensity is modeled with two nonradiative thermal activation energies, of which ET1 is dominant for about T⩽60 K, and ET2 for the upper temperature range of the measurement. The size of ET1 is invariably of the order of a few meV and, although of unclear origin, its magnitude is usually interpreted as an electronic energy level difference over which the carriers escape by thermal excitation. In CdTe the existence of such a small energy level difference ET1 is not easy to explain. On the contrary, we find clear evidence that, at low temperature, the PL intensity reduction with increasing temperature in fact results from the approximately T−2 temperature dependent capture cross sections of the carriers at the recombination centers, and not from a genuine thermal activation energy ET1.

/pdf/does-the-low-temperature-arrhenius-plot-of-the-29m142kkw1.pdf

Does the low-temperature Arrhenius plot of the photoluminescence intensity in CdTe point towards an erroneous activation energy?

Radiative recombination in Cu2ZnSnSe4 monograins studied by photoluminescence spectroscopy

In this study, we investigated the photoluminescence (PL) properties of Cu2ZnSnS4 polycrystals. Two PL bands at 1.27 eV and 1.35 eV at T = 10 K were detected. Similar behaviour with temperature and excitation power was found for both PL bands and attributed to the band-to-impurity recombination. Interestingly, the thermal activation energies determined from the temperature dependence of the PL bands coincide. With the support of the Raman results, we propose that the observed PL bands arise from the band-to-impurity-recombination process involving the same deep acceptor defect with ionization energy of around 280 meV but different Cu2ZnSnS4 phase with different bandgap energy.

/pdf/the-role-of-structural-properties-on-deep-defect-states-in-4h1p79583u.pdf

Jüri Krustok

Papers

Cu2Zn1–xCdx Sn(Se1–ySy)4 solid solutions as absorber materials for solar cells

Photoluminescence and Raman study of Cu2ZnSn(SexS1 − x)4 monograins for photovoltaic applications

Does the low-temperature Arrhenius plot of the photoluminescence intensity in CdTe point towards an erroneous activation energy?

Radiative recombination in Cu2ZnSnSe4 monograins studied by photoluminescence spectroscopy

The role of structural properties on deep defect states in Cu2ZnSnS4 studied by photoluminescence spectroscopy