Hidden polymorphism of FAPbI3 discovered by Raman spectroscopy

Formamidinium lead iodide FAPbI3 can be used in its cubic, black form as a light absorber material in single junction solar cells. It has a band gap 1.5 eV close to the maximum of the Shockley Queisser limit, and reveals a high absorption coefficient. Its high thermal stability up to 320 C has also a downside, which is the instability of the photo active form at room temperature RT . Thus, the black amp; 945; phase transforms at RT with time into a yellow non photo active amp; 948; phase. The black phase can be recovered by annealing of the yellow state. In this work, a polymorphism of the amp; 945; phase at room temperature was found as synthesized amp; 945;i , degraded amp; 945; amp; 948; and thermally recovered amp; 945;rec . They differ in the Raman spectra and PL signal, but not in the XRD patterns. Using temperature dependent Raman spectroscopy, we identified a structural change in the amp; 945;i polymorph at ca. 110 C. Above 110 C, the FAPbI3 structure has undoubtedly cubic Pm[3 with combining macron]m symmetry high temperature phase amp; 945;HT . Below that temperature, the amp; 945;i phase was suggested to have a distorted perovskite structure with Im[3 with combining macron] symmetry. Thermally recovered FAPbI3 amp; 945;rec also demonstrated the structural transition to amp; 945;HT at the same temperature ca. 110 C during its heating. The understanding of hybrid perovskites may bring additional assets in the development of new and stable structure

Water assisted nitrogen mediated crystallisation of ZnO films

Nitrogen mediated crystallisation NMC being performed in oxygen atmosphere at T amp; 8805;600 C is an effective approach to obtain very well 00l textured ZnO films. A use of NMC seed layers remarkably improves electrical transport properties of subsequently deposited ZnO Al contacts. In thiswork, crystallisation of quasi amorphous, nitrogen doped ZnO seed layers has been performed using water vapours at overpressure and temperatures around 100 C. This approach allows employment of soda lime float glass or temperature sensitive film stacks as a substrate. We propose here possible mechanism of water assisted NMC and grope for optimised crystallisation conditions on the basis of optical, microscopic, and textural investigation. Low temperature water assisted crystallisation of 20 nm thick ZnO layers was compared with high temperature annealing methods in terms of composition, microstructure and crystallinity. Electrical properties such as electron Hallmobility amp; 956;e , concentration of free electrons Ne and sheet resistance Rsh have been evaluated and compared for functional ZnO Al films obtained on glass and on differently crystallised NMC seed layers. It was found that the crystallised withwater assistance at lowtemperature ZnO seed layers provide comparable improvement in crystallinity and electrical properties of subsequently grown functional ZnO Al films with respect to the ones crystallised at high temperature. Use of optimised water assisted crystallisation of seed layers has allowed decreasing Rsh of thin 130 270 nm functional ZnO Al films twice compared to the glass substrate. Both provide this effect increase in amp; 956;e and increase of N

IC security and quality improvement by protection of chip backside against hardware attacks

In this work, a protection structure for the silicon chip backside will be presented, which is a protective Ti0 2 Ti Ti02 layer stack with an angular dependent reflectivity. It uses a selected p n junction as the light emitter and other junctions as photodetectors of the light reflected in various angles inside the silicon. The measurement of this structure highlights strong angle dependent reflectivity for the light reflected off the backside of the chip. Detecting these photocurrents indicates whether the IC backside is subject to a hardware attack that violates the backside layer integrity, like Fm, or preparative darnage of the layer. Creating a pattern of photocurrent ratios when the IC is running can signal the IC whether such physical attacks from the backside have occurred. Forthis protection concept, there is no need to add additional masks or circuitry of the IC, since it could use the drain or source junctions of transistors already availabl

Sputtered Zn O,S In2O3 H window layers for enhanced blue response of chalcopyrite solar cells

A combination of undoped ZnO and ZnO Al is the most commonly used window layer stack for chalcopyrite solar cells. The high carrier density and thickness required to achieve a sufficiently low sheet resistance lead to optical absorption and cause losses in photocurrent, in particular in monolithically interconnected modules. Additionally, the band gap of the CdS buffer layer and of un doped ZnO limit the blue response. These losses could be avoided by using a transparent conductive oxide with high carrier mobility and wider band gap in combination with a buffer layer which also has a wide band gap. We propose a stack of Zn O,S and In2O3 H and report on our first results concerning its implementation. This stack is Cd free, highly transparent over a wide range, and can be deposited completely by sputtering which is an industrially proven dry proces

Elucidating the Effect of the Different Buffer Layers on the Thermal Stability of CIGSe Solar Cells

In this contribution, the impact of thermal stress on Cu In,Ga Se 2 CIGSe thin film photovoltaic devices is investigated. The tolerance of such devices to high temperatures is of particular interest for processing transparent conductive oxides TCOs in order to further close the gap to the theoretical efficiency limit and for their potential use as bottom devices in tandem applications in order to overcome the theoretical efficiency limit of single junction solar cells. When CdS buffered CIGSe high efficiency solar cells are subjected to thermal stress, elemental interdiffusion of Na and Cd between the absorber and the window layers as well as chemical reactions at the CIGSe CdS interface result in a degraded power conversion efficiency PCE . Here, we compare the degradation mechanisms of CdS and GaO x buffered CIGSe solar cells under thermal stress. A model explaining the observed degradation behaviors is propose

Crystallisation phenomena of In₂O₃:H films

The crystallisation of sputter-deposited, amorphous In₂O₃:H films was investigated. The influence of deposition and crystallisation parameters onto crystallinity and electron hall mobility was explored. Significant precipitation of metallic indium was discovered in the crystallised films by electron energy loss spectroscopy. Melting of metallic indium at ~160 °C was suggested to promote primary crystallisation of the amorphous In₂O₃:H films. The presence of hydroxyl was ascribed to be responsible for the recrystallization and grain growth accompanying the inter-grain In-O-In bounding. Metallic indium was suggested to provide an excess of free electrons in as-deposited In₂O₃: and In₂O₃:H films. According to the ultraviolet photoelectron spectroscopy, the work function of In₂O₃:H increased during crystallisation from 4 eV to 4.4 eV, which corresponds to the oxidation process. Furthermore, transparency simultaneously increased in the infrared spectral region. Water was queried to oxidise metallic indium in UHV at higher temperature as compared to oxygen in ambient air. Secondary ion mass-spectroscopy results revealed that the former process takes place mostly within the top ~50 nm. The optical band gap of In₂O₃:H increased by about 0.2 eV during annealing, indicating a doping effect. This was considered as a likely intra-grain phenomenon caused by both (In⁰)o•• and (OH⁻)o• point defects. The inconsistencies in understanding of In₂O₃:H crystallisation, which existed in the literature so far, were considered and explained by the multiplicity and disequilibrium of the processes running simultaneously