Origin of Interface Limitation in Zn(O,S)/CuInS2-Based Solar Cells.

Copper indium disulfide (CuInS2) grown under Cu-rich conditions exhibits high optical quality but suffers predominantly from charge carrier interface recombination, resulting in poor solar cell performance. An unfavorable "cliff"-like conduction band alignment at the buffer/CuInS2 interface could be a possible cause of enhanced interface recombination in the device. In this work, we exploit direct and inverse photoelectron spectroscopy together with electrical characterization to investigate the cause of interface recombination in chemical bath-deposited Zn(O,S)/co-evaporated CuInS2-based devices. Temperature-dependent current-voltage analyses indeed reveal an activation energy of the dominant charge carrier recombination path, considerably smaller than the absorber bulk band gap, confirming the dominant recombination channel to be present at the Zn(O,S)/CuInS2 interface. However, photoelectron spectroscopy measurements indicate a small (0.1 eV) "spike"-like conduction band offset at the Zn(O,S)/CuInS2 interface, excluding an unfavorable energy-level alignment to be the prominent cause for strong interface recombination. The observed band bending upon interface formation also suggests Fermi-level pinning not to be the main reason, leaving near-interface defects (as recently observed in Cu-rich CuInSe2) as the likely reason for the performance-limiting interface recombination.

Waste- and Cd-Free Inkjet-Printed Zn(O,S) Buffer for Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells.

Thin film semiconductors grown using chemical bath methods produce large amounts of waste solvent and chemicals that then require costly waste processing. We replace the toxic chemical bath deposited CdS buffer layer from our Cu(In,Ga)(S,Se)2 (CIGS)-based solar cells with a benign inkjet-printed and annealed Zn(O,S) layer using 230 000 times less solvent and 64 000 times less chemicals. The wetting and final thickness of the Zn(O,S) layer on the CIGS is controlled by a UV ozone treatment and the drop spacing, whereas the annealing temperature and atmosphere determine the final chemical composition and band gap. The best solar cell using a Zn(O,S) air-annealed layer had an efficiency of 11%, which is similar to the best conventional CdS buffer layer device fabricated in the same batch. Improving the Zn(O,S) wetting and annealing conditions resulted in the best device efficiency of 13.5%, showing the potential of this method.

Micro-sized thin-film solar cells via area-selective electrochemical deposition for concentrator photovoltaics application.

Micro-concentrator solar cells enable higher power conversion efficiencies and material savings when compared to large-area non-concentrated solar cells. In this study, we use materials-efficient area-selective electrodeposition of the metallic elements, coupled with selenium reactive annealing, to form Cu(In,Ga)Se2 semiconductor absorber layers in patterned microelectrode arrays. This process achieves significant material savings of the low-abundance elements. The resulting copper-poor micro-absorber layers' composition and homogeneity depend on the deposition charge, where higher charge leads to greater inhomogeneity in the Cu/In ratio and to a patchy presence of a CuIn5Se8 OVC phase. Photovoltaic devices show open-circuit voltages of up to 525 mV under a concentration factor of 18 ×, which is larger than other reported Cu(In,Ga)Se2 micro-solar cells fabricated by materials-efficient methods. Furthermore, a single micro-solar cell device, measured under light concentration, displayed a power conversion efficiency of 5% under a concentration factor of 33 ×. These results show the potential of the presented method to assemble micro-concentrator photovoltaic devices, which operate at higher efficiencies while using light concentration.

Continuous-wave laser annealing of metallic layers for CuInSe2 solar cell applications: effect of preheating treatment on grain growth.

Ultra-fast thermal annealing of semiconductor materials using a laser can be revolutionary for short processing times and low manufacturing costs. Here we investigate Cu-In-Se thin films as precursors for CuInSe2 semiconductor absorber layers via laser annealing. The reaction mechanism of laser annealed metal stacks is revealed by measuring ex situ X-ray diffractograms, Raman spectra and composition. It is shown that the formation of CuInSe2 occurs via the formation of Cu x Se/In x Se y binary phases as in conventional annealing routes, despite the entirely different annealing time scale. Pre-alloying the Cu and In metals prior to laser annealing significantly enhances the selenisation reaction rate. Laser annealing for six seconds approaches a near phase-pure material, which exhibits similar crystalline quality to the reference material annealed for ninety minutes in a tube furnace. The estimated quasi Fermi level splitting deficit for the laser annealed material is only 60 meV lower than the reference sample, which implies a high optoelectronic quality.

Gallium In-Depth Profile in Bromine- Etched Copper-Indium-Galium-(Di)selenide (CIGS) Thin Films Inspected Using Raman Spectroscopy.

In the thin film solar cells domain, copper indium galium (di)selenide (CIGS) is a material with well-established photovoltaic purpose. Here the presence of a suitable [Ga]/([Ga]+[In]) (GGI) in-depth profile has proved to play a key role in the performance of cells. The implementation of a routine method based on reliable but easily available experimental techniques is mandatory to obtain information on the GGI profile of any CIGS layer, in order to achieve high efficiency chalcogenide layers. In this vein, we here propose and systematically test a simple method for the GGI profile determination based on repeated bromine etching of CIGS thin films followed by Raman analysis of the A1 peak position. The reliability of the proposed approach is verified using a methodical comparison with energy-dispersive X-ray spectroscopy (EDS) analysis and secondary ion mass spectroscopy (SIMS) profiles, showing a good agreement with the GGI in-depth profiles determined using Raman analysis on bromine etched samples.

Alternative Therapies in the Treatment of Atrial Fibrillation.

Atrial fibrillation (AF) is the most common clinical arrhythmia and represents a major social and economic problem. The number of subjects with AF is constantly increasing as a result of aging and improved survival in several cardiac and non-cardiac diseases. Patients with AF are often symptomatic, have a reduced physical capacity and are at high risk for thromboembolic events. Moreover, AF is associated with increased mortality and independent of the management, based either on rhythm or rate control strategy. The safety and efficacy of most anti-arrhythmic drugs are questionable. Increasing attention has therefore been addressed to evaluate the possible therapeutic and/or preventive effects of forms of treatment coming from ancient medical traditions of Far East, like acupuncture and yoga. In traditional Chinese medicine, acupuncture has been found effective in managing patients with paroxysmal supraventricular tachycardia. Recently, also in the Western literature, reports have been published supporting the clinical efficacy of acupuncture to treat arterial hypertension and to reduce chest pain. Other studies have evaluated the effects of acupuncture and other methods of Eastern Medicine, i.e., Qigong, Tai Chi Chuan and Yoga, in the treatment of cardiac illnesses associated with supraventricular arrhythmias. Two reports on the effects of acupuncture in preventing or reducing the rate of AF recurrences in patients with persistent or paroxysmal AF have been recently reported . Another ancient traditional eastern form of therapy and prevention, i.e., yoga, has been recently shown to reduce episodes of atrial fibrillation and improve the symptoms of anxiety and depression often associated with this arrhythmia. Growing evidence indicates that acupuncture and yoga are safe, without any pro-arrhythmic effect and with limited cost. All these factors should be considered when evaluating the efficacy of therapeutic intervention for an epidemic disease such as AF.

Acupuncture for paroxysmal and persistent atrial fibrillation: An effective non-pharmacological tool?

In Traditional Chinese Medicine, stimulation of the Neiguan spot has been utilized to treat palpitations and symptoms related to different cardiovascular diseases. We evaluated whether acupuncture might exert an antiarrhythmic effect on patients with paroxysmal or persistent atrial fibrillation (AF). Two sets of data are reviewed. The first included patients with persistent AF who underwent electrical cardioversion to restore sinus rhythm. The second included patients with symptomatic paroxysmal AF. All subjects had normal ventricular function. Acupuncture treatment consisted of 10 acupuncture sessions on a once a week basis with puncturing of the Neiguan, Shenmen and Xinshu spots. In patients with persistent AF, the recurrence rate after acupuncture treatment was similar to that observed in patients on amiodarone, but significantly smaller than that measured after sham acupuncture treatment or in the absence of any antiarrhythmic drugs. In a small group of patients with paroxysmal AF, acupuncture resulted in a significant reduction in the number and duration of symptomatic AF episodes. In conclusion, we observed that acupuncture of the Neiguan spot was associated with an antiarrhythmic effect, which was evident in patients with both persistent and paroxysmal AF. These preliminary data, observed in 2 small groups of AF patients, need to be validated in a larger population but strongly suggest that acupuncture may be an effective non-invasive and safe antiarrhythmic tool in the management of these patients.

Efficacy of acupuncture in preventing atrial fibrillation recurrences after electrical cardioversion.

INTRODUCTION: In traditional Chinese medicine, stimulation of the Neiguan spot has been utilized to treat palpitations. We evaluated whether acupuncture might prevent or reduce the rate of arrhythmia recurrences in patients with persistent atrial fibrillation (AF). METHODS AND RESULTS: We studied 80 patients with persistent AF after restoring sinus rhythm with electrical cardioversion. Twenty-six subjects who were already on amiodarone treatment constituted the AMIO reference group. The remaining patients were randomly allocated to receive acupuncture (ACU group, n = 17), sham acupuncture (ACU-sham group, n = 13), or neither acupuncture nor antiarrhythmic therapy (CONTROL group, n = 24). Patients in the ACU and ACU-sham groups attended 10 acupuncture sessions on a once-a-week basis. Only in the former group the Neiguan, Shenmen, and Xinshu spots were punctured. During a 12-month follow-up, AF recurred in 35 patients. Cumulative AF recurrence rates in the AMIO, ACU, ACU-sham, and CONTROL patients were 27%, 35%, 69%, and 54%, respectively (P = 0.0075, log-rank test). Ejection fraction (P = 0.0005), hypertension (0.0293), and left atrial diameter (P = 0.0361) were also significantly associated with AF recurrence. Compared with AMIO group, recurrence rate was similar in ACU patients (hazard ratio: 1.15, 95% CI: 0.38-3.49; P = 0.801) but significantly higher in ACU-sham and CONTROL patients (3.77, 1.39-10; P = 0.009 and 3.15, 1.23-8.06; P = 0.017, respectively) after adjustment for ejection fraction, hypertension, and left atrial diameter using Cox modeling. CONCLUSION: Our data indicate that acupuncture treatment prevents arrhythmic recurrences after cardioversion in patients with persistent AF. This minimally invasive procedure was safe and well tolerated.