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A few studies have reported on recurrent myocarditis occurring more than twice in one patient. In this study, we present a recurrent "third time" acute myocarditis in a young female Japanese patient with a history of a definitive diagnosis of lymphocytic myocarditis by endomyocardial biopsy, cardiac magnetic resonance imaging (CMR), and catheter examination twice in the past. Although chest pain and an increase in the cardiac enzymes were observed the third time, no significant changes were noted in the 12-lead electrocardiogram (ECG), and a definitive diagnosis could be achieved by CMR. This case suggested that in patients with a history of myocarditis, if there is chest pain and elevated cardiac enzymes even without any changes in the 12-lead ECG, acute myocarditis should be considered, and CMR is useful for the differentiation.Only four case reports including this present case were found through the previous literatures. More than two recurrent episodes of myocarditis have been extremely rare, but all cases have typical chest symptoms and a troponin level increase, leading to a relatively benign prognosis.

Chronological changes in ablation lesions after cryoballoon ablation (CBA) and hot balloon ablation (HBA) of atrial fibrillation (AF) remain unclear.Of 90 patients who underwent initial balloon-based catheter ablation of AF and cardiac magnetic resonance imaging (cMRI) 3 months after ablation, data from 48 propensity score-matched patients (24 per group; 34 males; age 62±10 years) were analyzed. High-density pulmonary vein-left antrum (PV-LA) voltage mapping was performed after PV isolation, and low voltage areas around the PV ostia were defined as the total acute ablation lesion area (cmThe %acute ablation lesion area was larger for the CBA group than for the HBA group (30.8±5.8% vs. 23.0±5.5%, p0.001). There was no difference in %chronic cMRI-derived ablation lesion area (24.8±10.8% vs. 21.1±11.6%, p = 0.26) between groups. The rates of chronic AF recurrence were 12.5% and 8.3%, respectively (p = 0.45; log-rank test). LA volume and LA surface area were strongly associated with AF recurrence, but %chronic ablation lesion area was not (27±8% vs. 23±12%, p = 0.39).Large acute ablation lesions after CBA were smaller during the chronic phase. The size of chronic ablation lesions and the rate of AF recurrence were both similar for CBA and HBA.

A few studies have reported on recurrent myocarditis occurring more than twice in one patient. In this study, we present a recurrent "third time" acute myocarditis in a young female Japanese patient with a history of a definitive diagnosis of lymphocytic myocarditis by endomyocardial biopsy, cardiac magnetic resonance imaging (CMR), and catheter examination twice in the past. Although chest pain and an increase in the cardiac enzymes were observed the third time, no significant changes were noted in the 12-lead electrocardiogram (ECG), and a definitive diagnosis could be achieved by CMR. This case suggested that in patients with a history of myocarditis, if there is chest pain and elevated cardiac enzymes even without any changes in the 12-lead ECG, acute myocarditis should be considered, and CMR is useful for the differentiation.Only four case reports including this present case were found through the previous literatures. More than two recurrent episodes of myocarditis have been extremely rare, but all cases have typical chest symptoms and a troponin level increase, leading to a relatively benign prognosis.

Objectives This study aimed to evaluate whether myocardial blood flow (MBF) quantified with dynamic computed tomography perfusion imaging (CTP) has an incremental prognostic value over coronary CT angiography (CTA) for major adverse cardiac events (MACEs) in patients with suspected coronary artery disease (CAD). Background The incremental prognostic value of CTP over CTA is unclear. The quantification of MBF with dynamic CTP may potentially enhance risk stratification. Methods A total of 332 patients (67% men; age: 67 ± 10 years) with suspected CAD who underwent CTA and dynamic CTP was analyzed. A MACE was defined as cardiac death, nonfatal myocardial infarction (MI), unstable angina, or hospitalization for congestive heart failure. A summed stress score (SSS) was calculated by adding scores of all myocardial segments according to normalized MBF values. Abnormal perfusion was defined as SSS ≥4. Obstructive CAD was defined as ≥50% stenosis in ≥1 vessel on CTA. Results During a median follow-up of 2.5 years, 19 patients had a MACE. Multivariate analysis showed that, when adjusted for obstructive CAD on CTA, abnormal perfusion was significantly associated with hazards for MACEs (hazard ratio [HR]: 5.7; 95% confidence interval [CI]: 1.9 to 16.9; p = 0.002), with a significant improvement in the prognostic value. Abnormal perfusion was an independent predictor even when adjusted for ≥70% stenosis in ≥1 vessel (HR: 5.4; 95% CI: 1.7 to 16.7; p = 0.003) or adjusted for ≥50% stenosis in ≥2 vessels (HR: 6.5; 95% CI: 2.2 to 18.9; p = 0.001). In the setting of obstructive CAD, annualized event rates showed a significant difference between the patients with and without abnormal perfusion for all events (12.2% vs. 1.5%; p = 0.002) and for cardiac death and nonfatal MI (4.2% vs. 0%; p = 0.015). Conclusions MBF quantified with dynamic CTP has an incremental prognostic value over CTA. The addition of dynamic CTP to CTA allows improved risk stratification of patients with CTA-detected stenosis.

Background The clinical efficacy of Impella for high-risk percutaneous coronary intervention and cardiogenic shock remains under debate. We thus sought to investigate the protective effects on the heart by the early use of Impella before percutaneous coronary intervention using cardiovascular magnetic resonance imaging (CMR). Methods We evaluated cardiac magnetic resonance imaging results in 22 broad anterior ST-elevation myocardial infarction cases between 2017 and 2019. A mechanical circulation system (Impella or intra-aortic balloon pump) was implanted before percutaneous coronary intervention if needed; all patients underwent cardiac magnetic resonance imaging 2 weeks later. Results There were 6 patients in the Impella group and 16 in the non-Impella group; no differences were found in the door-to-balloon time (60 ± 17 vs. 58 ± 25 min, P = 0.58), peak creatine kinase (7922 ± 4864 vs. 6950 ± 4801 IU/L, P = 0.74), and hospital admission days (28 ± 8 vs. 25 ± 7 days, P = 0.40) between the two groups; however, cardiac magnetic resonance imaging-derived left ventricular end-diastolic volume was significantly smaller in the Impella group (140.6 ± 28 vs. 182.5 ± 45 ml, P = 0.004). Overall diastolic strain rate (SR) at the non-infarcted area in the IMPELLA group was significantly higher as compared to non IMPELLA group (longitudinal diastolic SR: 1.1 ± 0.4 vs 0.7 ± 0.3 S− 1, P = 0.04, radial diastolic SR: -1.8 ± 0.4 vs -1.1 ± 0.4 S− 1, P = 0.004, circumferential diastolic SR: 1.0 ± 0.1vs 0.6 ± 0.2 S− 1, P = 0.001). Conclusions Early implantation of Impella before percutaneous coronary intervention for anterior ST-elevation myocardial infarction acutely prevented enlargement of left ventricular end-diastolic volume and worsening of diastolic SR in the remote myocardium. This study provides clinical insight into understanding the usefulness of Impella to prevent future heart failure.

Atrial fibrillation (AF) is a progressive disease that starts with structural or functional changes in the left atrium and left ventricle, and evolves from paroxysmal toward sustained forms. Early detection of structural or functional changes in the left atrium and left ventricle in the paroxysmal stage could be useful for identifying higher risk of progression to persistent AF and future cardio-cerebrovascular events. The aim of this study was to test the hypothesis that feature tracking (FT) left atrial (LA) strain and left ventricular (LV) extracellular volume fraction (ECV) derived from cardiovascular magnetic resonance (CMR) could detect the early changes of remodeling in the left atrium and ventricle in the stage of paroxysmal AF (PAF).Participants comprised 106 PAF patients (age, 66.1 ± 10.7 years; 66% male) who underwent clinical CMR before pulmonary vein isolation and 20 control subjects (age, 68.3 ± 8.6 years; 55% male). CMR-FT LA strain/phasic function and LV-ECV were compared between the PAF and control groups. Total and passive LA empty fraction (LAEF) and LA strain (corresponding to LA reservoir and conduit function) were decreased in the PAF group compared to the control group. However, active LAEF (corresponding to LA booster pump function) did not differ significantly between the PAF group (33.9 ± 10.9%) and control group (37.9 ± 13.3%, p = 0.15), while active LA strain (corresponding to LA booster pump function) was significantly decreased in the PAF group (11.4 ± 4.3 vs. 15.2 ± 5.6%, p = 0.002). LV-ECV was significantly greater in the PAF group (28.7 ± 2.8%) than in the control group (26.6 ± 2.0%, p = 0.002). In the PAF group, LV-ECV correlated significantly with E/e’ and LA volume index. Regarding LA strain, correlations were seen between LV-ECV and both reservoir function and conduit function.CMR-FT LA strain in combination with LV-ECV offers a potential imaging marker that identifies LA/LV remodeling including subtle LA booster pump dysfunction undetectable by conventional booster pump LAEF in the stage of PAF. These findings provide new insights into LA-LV interactions and further investigation regarding association between perpetuation of AF and LA functional remodeling in PAF patients.

Atrial fibrillation (AF) is a progressive disease that starts with structural or functional changes in the left atrium and left ventricle, and evolves from paroxysmal toward sustained forms. Early detection of structural or functional changes in the left atrium and left ventricle in the paroxysmal stage could be useful for identifying a higher risk of progression to persistent AF and future cardio-cerebrovascular events. The aim of this study was to test the hypothesis that the feature tracking (FT) left atrial (LA) strain and left ventricular (LV) extracellular volume fraction (ECV) derived from cardiovascular magnetic resonance (CMR) could detect early changes in remodeling of the left atrium and ventricle in the paroxysmal AF (PAF) stage. The participants were comprised of 106 PAF patients (age, 66.1 ± 10.7 years; 66% male) who underwent clinical CMR before pulmonary vein isolation and 20 control subjects (age, 68.3 ± 8.6 years; 55% male). The CMR-FT LA strain/phasic function and LV-ECV were compared between the PAF and control groups. The total and passive LA empty fraction (LAEF) and LA strain (corresponding to LA reservoir and conduit function) were decreased in the PAF group as compared to the control group. However, active LAEF (corresponding to the LA booster pump function) did not differ significantly between the PAF group (33.9 ± 10.9%) and control group (37.9 ± 13.3%, p = 0.15), while the active LA strain (corresponding to the LA booster pump function) was significantly decreased in the PAF group (11.4 ± 4.3 vs. 15.2 ± 5.6%, p = 0.002). The LV-ECV was significantly greater in the PAF group (28.7 ± 2.8%) than control group (26.6 ± 2.0%, p = 0.002). In the PAF group, the LV-ECV correlated significantly with the E/e′ and LA volume index. Regarding the LA strain, correlations were seen between the LV-ECV and both the reservoir function and conduit function. CMR-FT LA strain in combination with the LV-ECV in a single clinical study offers a potential imaging marker that identifies LA/LV remodeling including subtle LA booster pump dysfunction undetectable by the conventional booster pump LAEF in the PAF stage.

Extent of myocardial fibrosis in hemodialysis patients has been associated with poor prognosis. Myocardial extracellular volume (ECV) quantification using contrast enhanced cardiac computed tomography (CT) is a novel method to determine extent of myocardial fibrosis. Cardiac CT-based myocardial ECV in hemodialysis patients with those of propensity-matched non-hemodialysis control subjects were compared. Twenty hemodialysis patients (mean age, 67.4 ± 9.6 years; 80% male) and 20 propensity-matched non-hemodialysis controls (mean age, 66.3 ± 9.1 years; 85% male) who underwent comprehensive cardiac CT consisted of calcium scoring, coronary CT angiography, stress perfusion CT and delayed enhancement CT were evaluated. Myocardial ECV was significantly greater in the hemodialysis group than in the control group (33.8 ± 4.7% versus 26.6 ± 2.9%; P r = 0.54; P = 0.01), while there was no correlation between myocardial ECV and other cardiac parameters including left ventricular mass index and severity of myocardial ischemia. Cardiac CT-based myocardial ECV may offer a potential imaging biomarker for myocardial fibrosis in HD patients.

Delayed enhancement cardiac CT is a potential tool for myocardial viability assessment and is essential for extracellular volume fraction (ECV) estimation with CT. The objective of this study is to determine the optimal delay time for acquisition of delayed CT scans. Thirty-five patients with enhancement pattern typical of previous myocardial infarction on delayed CT and 17 control subjects comprised the study population. Delayed scans were acquired at 3, 5 and 7 min after contrast material injection. Image quality and estimated ECV were compared among the three time points. Delayed CT at 5 min showed the highest signal-to-noise ratio of 15.2 ± 1.0 [p

Atomic layer deposition of Al2O3 was used to fabricate rear surface passivation with lithographed point contact Cu(In,Ga)Se2 (CIGS) solar cells. We successfully demonstrated the use of photolithography to fabricate point contact holes of small size and fine pitch. The efficiency of the Al2O3 rear-surface-passivated ultra-thin CIGS solar cells with absorber layers of 1.89 μm and with a 5-nm-thick Al2O3 rear surface passivation layer and local point contact holes with a pitch of 1 μm and a diameter of 500 nm was 19.3% (total area = 0.519 cm2). The efficiency of the Al2O3 rear-surface-passivated ultra-thin CIGS solar cells with absorber layers of 380 nm was 11.3% (active area = 0.514 cm2) when an antireflection layer was used. Compare with unpassivated CIGS solar cells, higher efficiencies were found for the Al2O3 rear-surface-passivated CIGS solar cells, mainly due to the reduced carrier recombination and enhanced rear internal light reflection.

B-doped ZnO (ZnO:B) films with improved visible and near-infrared transparency have been applied as transparent conductive oxide (TCO) electrodes in Cu(In,Ga)Se2 submodules. The use of ZnO:B instead of conventional Al-doped ZnO (ZnO:Al) improved the short-circuit current density (Jsc) and the resulting conversion efficiency without decreasing the fill factor. The detailed optical and electrical analysis of the modules revealed that (i) the improvement in Jsc was due to lower parasitic absorption owing to free carriers in the TCO layer and (ii) the series resistance of the ZnO:B module originating from the TCO and TCO/Mo contacts is comparable to that of the ZnO:Al module.

Background Recent studies using stress‐rest perfusion cardiovascular magnetic resonance ( CMR ) demonstrated a close correlation between myocardial ischemia and reduced fractional flow reserve ( FFR ). However, its diagnostic concordance may be reduced in patients with multivessel disease. We sought to evaluate the concordance of adenosine stress‐rest perfusion CMR for predicting reduced FFR , and to determine the additive value of measuring global coronary flow reserve ( CFR ) in the coronary sinus in multivessel disease. Methods and Results Ninety‐six patients with angiographic luminal narrowing >50% underwent comprehensive CMR study and FFR measurements in 139 coronary vessels. FFR CFR was quantified as the ratio of stress‐rest coronary sinus flow measured by phase‐contrast cine CMR . In 25 patients with single‐vessel disease, visual assessment of perfusion CMR yielded high diagnostic concordance for predicting flow‐limiting stenosis, with the area under receiver operating characteristic curve of 0.93 on a per‐patient basis. However, in 71 patients with multivessel disease, perfusion CMR underestimated flow‐limiting stenosis, resulting in the reduced area under receiver operating characteristic curve of 0.74. When CFR of P =0.002). Conclusions Visual analysis of stress‐rest perfusion CMR has limited concordance with FFR in patients with multivessel disease. Multiparametric CMR integrating stress‐rest perfusion CMR and flow measurement in the coronary sinus is useful for detecting reduced FFR in multivessel disease.

A transparent amorphous oxide semiconductor (TAOS) layer for the suppression of interface recombination and enhancement of open-circuit voltage ( $V_{{\rm oc}}$ ) in Cu(In,Ga)Se2 (CIGS) solar cells is demonstrated. A 60-nm-thick n-type a-In2−2 $_{{x}}$ Ga2 $_{{x}}$ O3 ( $x\! =\! 0.6, 0.7, 0.8, 0.9, 1$ ) or a-Ga2−2 $_{{y}}$ Al2 $_{{y}}$ O3 ( $y = 0.1, 0.2$ ) layer was introduced between the CIGS film and the ZnO transparent front contact. The solar cell performance systematically varied as a function of x and y , and CIGS solar cells with a-In2−2 $_{{x}}$ Ga2 $_{{x}}$ O3 ( $x = 0.9, 1$ ) buffer layers showed $V_{{\rm oc}}$ values comparable with those of a reference cell with standard i-ZnO/CdS buffer layers. Current density–voltage (J–V) curve behavior can be explained by conduction band discontinuity at the TAOS/CIGS interface and the carrier density of the TAOS layer.

Simultaneous realization of high values of open circuit voltage (Voc), fill factor (FF), and energy conversion efficiency (η) in wide-gap CuGaSe2 (CGS) solar cells has long been one of the most challenging issues in the realm of chalcopyrite photovoltaics. In this communication, structural tuning of CGS thin films by means of controlling the amount of Se flux used during CGS film growth and improvements in solar cell performance (Voc > 0.9 V, FF > 0.7, and η > 10%) are demonstrated. Systematic variations in CGS film properties with the Se flux and correlation with device properties are shown. The unique CGS thin-film growth kinetics, which are different from narrow-gap Cu(In,Ga)Se2, are also presented and discussed. This development of double digit efficiency for CGS solar cells opens a new frontier for the broad application of a new class of chalcopyrite-based devices. Copyright © 2014 John Wiley & Sons, Ltd.

The relationship between the composition and conversion efficiency of Cu 2 ZnSnSe 4 (CZTSe)-based solar cells was investigated. CZTSe films were grown by thermal deposition using a coevaporation method. It was found that the composition of CZTSe and Na concentration [Na] have strong correlations to the conversion efficiency, and higher-efficiency samples were obtained with the composition ratios closer to Zn/Sn ~ 1.6, Cu/(Zn + Sn) ~ 0.8, and [Na] ~ 2%. The highest conversion efficiency ( η = 2.1%) was obtained in the composition region, and the composition was significantly nonstoichiometric. The CZTSe composition was automatically fixed on a tie line between Cu 2 ZnSnSe 4 and ZnSe, and it was demonstrated that this composition can be expressed by one parameter. The structural and electrical properties of the high- and low-efficiency samples were also investigated. No significant differences in such properties were observed between the high- and low-efficiency samples by surface, x-ray diffraction, and Raman measurements. However, the low-efficiency sample showed a high carrier concentration.

In this paper, we report a recent progress in Cu(In,Ga)Se2 (CIGS) solar cells and mini-modules demonstrated on soda-lime glass (SLG) substrates, which are one of the most common and cost effective substrate materials for chalcopyrite photovoltaics. CIGS absorber layers grown by the three-stage co-evaporation process was used with an optimized [Se]/[metal] flux ratio and preferable substrate temperatures for SLG substrate thicknesses. SLG substrates of 0.28–1.1 mm in thickness, which are thinner than that generally used in laboratories and industries (∼2–3 mm), were employed to develop techniques for further reductions of material cost and module weight. Solar cell and mini-module efficiencies of >19% and >17%, respectively, with relatively high open circuit voltages (Voc) and fill factors (FF) (Voc 0.77 V and FF 0.79 for cells, and Voc 0.77 V and FF 0.74 for mini-modules) were demonstrated using a composition ratio [Ga]/([In]+[Ga]) of 0.45 for the CIGS absorber layers. Key techniques and future directions toward highly efficient CIGS solar cells and modules with high values of Voc and FF are discussed.

CIGS solar cells were fabricated on a hybrid back contact comprised of a TCO layer (ZnO:Ga (GZO)) and Mo layers. It was discovered that an additional Mo layer introduced underneath the TCO layer promotes sodium diffusion through the TCO back contact into the upper CIGS absorber layer. Improvement in VOC and JSC values relative to those of sodium-free solar cells was achieved with the Mo/GZO/Mo hybrid back contact as a result of the enhanced sodium diffusion.

The approaches and achievements in the development of high-efficiency CuInGaSe2 (CIGS) monolithically integrated submodules will be reported. Two types of techniques, the conventional (batch-process) and the in-line three-stage evaporation techniques, have been employed to deposit high-quality CIGS absorbers on 10 × 10-cm Mo/soda lime glass substrates. CIGS films deposited by both the conventional and the in-line evaporation techniques showed an in-depth compositional grading of In and Ga (referred as the double graded bandgap) which is a fingerprint of the three-stage evaporation process. The optimization of the integration processes such as mechanical scribing, as well as the improvement in electrical and optical properties of ZnO window layers, made possible the demonstration of high-efficency CIGS submodules with efficiencies as high as η = 16.6% (aperture area: 67.2 cm2) and η = 15.8% (aperture area: 76.5 cm2) for the conventional and the in-line evaporation process, respectively. Copyright © 2012 John Wiley & Sons, Ltd.

Texture and morphology variations in co-evaporated (In,Ga)2Se3 and Cu(In,Ga)Se2 (CIGS) films grown with various Se source conditions during growth were studied. The Se species of simply evaporated, large molecular Se (E-Se, low-sticking coefficient), and RF-plasma cracked atomic Se (R-Se, high sticking coefficient) were used in the present work. (In,Ga)2Se3 precursor films, which were prepared during the first stage of CIGS film growth by the three-stage process, showed systematic variations in texture and Na distribution profile with varying evaporative Se (E-Se) flux. The properties of CIGS films and solar cells also showed systematic variations, and the open-circuit voltage (Voc) and fill factor were found to be especially sensitive to the E-Se flux. R-Se grown (In,Ga)2Se3 precursor films featured granular morphology with strong (105) and (301) peaks in the diffraction pattern, and the texture was very similar to an E-Se grown film fabricated with a Se to group III metal (In + Ga) flux ratio (P[Se]/[In + Ga]) of about 6, although the nominal P[Se]/[In + Ga] used for an R-Se source was very small and less than 0.5. The R-Se grown CIGS films displayed, however, highly dense surfaces and larger grain sizes than E-Se grown CIGS films. The controllability of film morphology and the Na diffusion profile in (In,Ga)2Se3 and CIGS films with various Se source conditions are discussed. Copyright © 2011 John Wiley & Sons, Ltd.

Coevaporated Cu(In,Ga)Se 2 (CIGS) film growth using a rf-plasma cracked Se-radical beam (R–Se) source leads to a significant reduction in the amount of raw Se source material wasted during growth and exhibits unique film properties such as highly dense, smooth surfaces and large grain size. R–Se grown CIGS solar cells also show concomitant unique properties different from conventional evaporative Se (E–Se) source grown CIGS cells. In the present work, the impact of modified surfaces, interfaces, and bulk crystal properties of R–Se grown CIGS films on the solar cell performance was studied. When a R–Se source was used, Na diffusion into CIGS layers was enhanced while a remarkable diffusion of elemental Ga and Se into Mo back contact layers was observed. Improvements in the bulk crystal quality as manifested by large grain size and increased Na concentration with the use of a R–Se source is expected to be effective to improve photovoltaic performance. Using a R–Se source for the growth of CIGS absorber layers at a relatively low growth temperature, we have successfully demonstrated a monolithically integrated submodule efficiency of 15.0% (17 cells, aperture area of 76.5 cm 2 ) on 0.25-mm thick soda-lime glass substrates.

Structural and electrical properties of polycrystalline CuGaSe2 thin films have been studied by changing the Ga/Cu ratio in the films. CuGaSe2 thin films with various Ga/Cu ratio were grown over Mo-coated soda-lime glass substrates. With the increase of Ga content in CuGaSe2, morphology of the films was found to deteriorate which is associated with the smaller grain size and the appearance of impurity phases presumably due to the phase transition from the chalcopyrite structure to the defect-related phase on the surface of the films. Properties of the Ga poor films were affected by the Cu rich secondary phases. Electrical properties of the films were strongly influenced by the structural properties and degraded with increasing the Ga/Cu ratio in the film. Device performances, fabricated with the corresponding CuGaSe2 films, were found to be correlated with the Ga/Cu ratio in the films and consistent with the observed structural and electrical properties.

Structural, electrical and optical properties of Al doped ZnO (Al:ZnO) thin film of various thicknesses, grown by radio-frequency magnetron sputtering system were studied in relation to the application as a window layer in Cu(In1−xGax)Se2 (CIGS) thin film solar cell. It was found that the electrical and structural properties of Al:ZnO film improved with increasing its thickness, however, the optical properties degraded. The short circuit current density, Jsc of the fabricated CIGS based solar cells was significantly influenced by the variation of the Al:ZnO window layer thickness. Best efficiency was obtained when CIGS solar cell was fabricated with electrically and optically optimized Al:ZnO window layer.

The influence of Se beam pressure on defect properties in Cu(In 1– x ,Ga x )Se 2 (CIGS)-based solar cells fabricated by the three-stage process was investigated by admittance spectroscopy. The Se beam pressure was varied from 1.3×10 −3 to 4.4×10 −3 Pa, at the position of the samples, by varying the Se cell temperature. The spectra for all samples show three distinct peaks denoted as α , β , and ζ with activation energies of 20, 150, and 300 meV, respectively. The trap density of ζ increased from 5×10 14 to 4×10 15 cm −3 with decrease in Se beam pressure; the trap densities of α and β did not change. These results suggest that the origin of ζ is related to the Se deficiency. The density of ζ seems to correlate with the cell efficiency. Therefore, it is important to control the Se beam pressure in order to obtain highly efficient solar cells.

Quantitative phase analysis of Cu(In 1− x Ga x )Se 2 (CIGS) thin film grown over Mo coated soda lime glass substrates was studied by Rietveld refinement process using room temperature X-ray data at θ –2 θ mode. Films were found to contain both stoichiometric Cu(In 1− x Ga x )Se 2 and defect related Cu(In 1− x Ga x ) 3 Se 5 phases. Best fitting was obtained using crystal structure with space group I-42d for Cu(In 1− x Ga x )Se 2 and I-42m for Cu(In 1− x Ga x ) 3 Se 5 phase. The effects of Ga/III (=Ga/In+Ga= x ) ratio and Se flux during growth over the formation of Cu(In 1− x Ga x ) 3 Se 5 defect phase in CIGS was studied and the correlation between quantity of Cu(In 1− x Ga x ) 3 Se 5 phase and solar cell performance is discussed.

Cu(In,Ga)Se 2 (CIGS) thin films were grown by the three-stage process using a rf-plasma cracked Se-radical beam source. CuGaSe 2 (CGS) films grown at a maximum substrate temperature of 550 °C and CuInSe 2 (CIS) and CIGS films grown at the lower temperature of 400 °C exhibited highly dense surfaces and large grain size compared with films grown using a conventional Se-evaporative source. This result is attributed to the modification of the growth kinetics due to the presence of active Se-radical species and enhanced surface migration during growth. The effect on CIGS film properties and solar cell performance has been investigated. Enhancements in the cell efficiencies of 400 °C-grown CIS and CIGS solar cells have been demonstrated using a Se-radical source.

We have successfully fabricated high-efficiency CuInGaSe 2 (CIGS) solar cells with CdS film deposited by ammonia-free process. The CdS films were formed on CIGS films by chemical bath deposition from an aqueous solution containing cadmium acetate and thioacetamide. The properties of CdS films deposited on soda lime glass were investigated by atomic force microscopy and optical transmission measurement. By optimizing the concentration of the solution used for the formation of CdS films and the thickness of i-ZnO films used for solar cell production, high-efficiency ammonia-free cells were fabricated. The properties of the ammonia-free cell fabricated by the optimized process were V OC = 0.695 V, J SC = 32.812 mA/cm 2 , FF = 0.755 and η = 17.22%. These values are comparable to those of the cells produced by the conventional process using ammonia.

Effects of Mo back contact thickness on the photovoltaic properties of CIGS solar cells were investigated. When the Mo was thin, an increase in series resistance and leakage current adversely affected the FF (fill factor) in solar cells fabricated using the Mo layers. On the other hand, when the thickness of the Mo layer was as thick as 0.8 μm, sodium out-diffusion from the SLG decreased. The resulting reduced sodium concentration in CIGS films grown on top of the contact layers resulted in reduced open circuit voltage (V OC ). As a consequence of the tradeoff between the decreased sodium diffusion for thicker Mo layers and reduced FF in thin Mo layers, the optimal Mo thickness was found to be 0.2 μm. Water vapor introduction during the deposition of the CIGS absorber layer was found to be effective in improving overall photovoltaic properties especially in solar cells with thin Mo back contacts. With water vapor introduction, cell efficiencies as high as 16.9% and 16.0% were obtained with Mo thicknesses of 0.2 μm and 0.07 μm, respectively.

Deep levels in Cu(In 1 − x ,Ga x )Se 2 (CIGS) are studied by transient photocapacitance (TPC) spectroscopy by varying the Ga concentration, x , from 0.38 to 0.7. The TPC spectra of CIGS thin-film solar cells at 140 K exhibited a defect level with an optical transition energy of about 0.8 eV. The spectrum shape in the sub-bandgap region is independent of the Ga concentration. Therefore, the optical transition energy to the defect level is almost constant with about 0.8 eV from the valence band. The TPC signals for defect level are quenched by increasing temperature. The activation energy of thermal quenching is estimated to be about 0.3 eV. The thermal and optical activation processes are explained using configuration coordinate diagram.

The effects of annealing under various atmospheres on the electrical properties of Cu(In,Ga)Se2 (CIGS) films and CdS/CIGS heterostructures were investigated. For CIGS films without CdS, the electrical properties of CIGS degraded under vacuum and O2 annealing, although such degradations were not observed under N2 annealing. For the CdS/CIGS heterostructures, the electrical properties of the junctions improved after annealing under all gas ambients. Therefore, CdS films prevent the chemical reactions at the CIGS surfaces and are necessary for effectively annealing the CIGS film. We observed a distinct correlation between the degradation of the electrical properties and increase in the defect density. Finally, we discussed the origin of the defect states.

Defect levels in Cu(In 1 − x ,Ga x )Se 2 (CIGS) were studied by using admittance spectroscopy with varying Ga concentration of x from 0.38 to 1.0. Two distinct peaks ( α and ζ ) were detected from all of CIGS samples. Peak α could be attributed to the shallow acceptors. Peak ζ was closely correlated with the surface potential of CIGS; therefore, it may have been caused by traps near the surface of CIGS such as grain boundary defects. The intensity of peak ζ increases with increasing Ga concentration. Further, this intensity was correlated with the ideality factor of the Al/CIGS Schottky junction. We suggest that the degradation of the performance of CIGS solar cell with increasing Ga concentration may be concerned with defects corresponding to peak ζ ˙

A drastic enhancement of electron mobility was observed in Zn polar ZnMgO/ZnO heterostructures (ZnMgO on ZnO) grown by radical source molecular beam epitaxy (MBE) due to the formation of a two-dimensional electron gas (2DEG). The electron mobility dramatically increased with increasing Mg composition for a ZnMgO layer and the electron mobility ( μ ∼ 250 cm 2 / Vs ) at RT reached a value more than twice that of an undoped ZnO layer ( μ ∼ 100 cm 2 / Vs ). Reflection high energy electron diffraction (RHEED) patterns taken during the growth of the ZnMgO layer remained streaky; X-ray diffraction measurements showed no evidence of phase separation for up 44% Mg composition. Temperature-dependent Hall measurements of ZnMgO/ZnO heterostructures also exhibited properties associated with well-defined heterostructures. The Hall mobility increased monotonically with decreasing temperature, reaching a value of 2750 cm 2 / Vs at 4 K. Zn polar “ZnMgO on ZnO” structures are easy to adapt to top-gate devices. These results open new possibilities for high electron mobility transistors (HEMTs) using ZnO-based materials.

We have studied the three-stage deposition process of CuIn1−xGaxSe2 (CIGS) thin films using spectroscopic light scattering (SLS), under varied deposition conditions. The structural changes of CIGS films by (1) Ga composition, (2) Se supply and (3) low deposition temperature, were observed in situ by SLS. The largest changes in SLS profiles by the Ga composition was observed between x = 0.3 and 0.5. The SLS profiles changed significantly during stage 1 by varying the Se pressure, while the temperature profiles did not.

The effects of water vapor introduction during the growth of Cu(In 1-x Ga x )Se 2 , specifically CuInSe 2 (CISe), Cu(In,Ga)Se 2 (CIGSe), and CuGaSe 2 (CGSe) thin films were studied. We have developed thus far a novel technique to improve CIGSe (x ∼ 0.5) cell performance by means of water vapor introduction during CIGSe deposition. In this study, we have examined the effectiveness of water vapor introduction for other x-compositions (CISe and CGSe). Variations in the electrical properties observed in CIGSe (x ∼ 0.5), that is, increasing hole density and conductivity with water vapor introduction, were also observed in CISe and CGSe. Water vapor introduction affected solar cell performance as well; open circuit voltages, short circuit current densities, and efficiencies were improved. The improvements in cell performance are thought to be related to annihilation of donor defects arising from Se-vacancies by incorporation of oxygen from the water vapor. In addition to this, the sodium content in the CIGSe layers was found to depend on the partial pressure of water vapor during deposition. This result suggests that the improvement mechanism is also related with the so-called 'Na-effects'.

The electrical properties of Al/Cu(In,Ga)Se2 (Al/CIGSe) Schottky junction and ZnO/CdS/CIGSe heterojunction were studied by admittance spectroscopy. Three distinct peaks (peaks α, ζ, and ϵ) were detected from all the CIGSe samples. The activation energies for the traps corresponding to peaks α and ζ were estimated to be approximately 10 meV and 300 meV, respectively. The peak α may be due to the shallow acceptor, and peaks ζ and ϵ may be due to defects in the CIGSe layer. The characteristics of the peak ζ have close correlation with the surface potential of the CIGSe layer. Therefore, the peak ζ may be caused by traps such as grain boundary defects near the surface of the CIGSe layer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)