The intensity of the infrared radiation emitted by objects is mainly a function of their temperature. In infrared thermography, this feature is used for multiple purposes: as a health indicator in medical applications, as a sign of malfunction in mechanical and electrical maintenance or as an indicator of heat loss in buildings. This paper presents a review of infrared thermography especially focused on two applications: temperature measurement and non-destructive testing, two of the main fields where infrared thermography-based sensors are used. A general introduction to infrared thermography and the common procedures for temperature measurement and non-destructive testing are presented. Furthermore, developments in these fields and recent advances are reviewed.

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Infrared thermography for temperature measurement and non-destructive testing.

Organic–inorganic hybrid perovskite solar cells with mixed cations and mixed halides have achieved impressive power conversion efficiency of up to 22.1%. Phase segregation due to the mixed compositions has attracted wide concerns, and their nature and origin are still unclear. Some very useful analytical techniques are controversial in microstructural and chemical analyses due to electron beam-induced damage to the “soft” hybrid perovskite materials. In this study photoluminescence, cathodoluminescence, and transmission electron microscopy are used to study charge carrier recombination and retrieve crystallographic and compositional information for all-inorganic CsPbIBr2 films on the nanoscale. It is found that under light and electron beam illumination, “iodide-rich” CsPbI(1+x)Br(2−x) phases form at grain boundaries as well as segregate as clusters inside the film. Phase segregation generates a high density of mobile ions moving along grain boundaries as ion migration “highways.” Finally, these mobile ions can pile up at the perovskite/TiO2 interface resulting in formation of larger injection barriers, hampering electron extraction and leading to strong current density–voltage hysteresis in the polycrystalline perovskite solar cells. This explains why the planar CsPbIBr2 solar cells exhibit significant hysteresis in efficiency measurements, showing an efficiency of up to 8.02% in the reverse scan and a reduced efficiency of 4.02% in the forward scan, and giving a stabilized efficiency of 6.07%.

Phase segregation enhanced ion movement in efficient inorganic CsPbIBr2 solar cells

Nine different types of shunt have been found in state-of-the-art mono- and multicrystalline solar cells by lock-in thermography and identified by SEM investigation (including EBIC), TEM and EDX. These shunts differ by the type of their I–V characteristics (linear or nonlinear) and by their physical origin. Six shunt types are process-induced, and three are caused by grown-in defects of the material. The most important process-induced shunts are residues of the emitter at the edge of the cells, cracks, recombination sites at the cell edge, Schottky-type shunts below grid lines, scratches, and aluminum particles at the surface. The material-induced shunts are strong recombination sites at grown-in defects (e.g., metal-decorated small-angle grain boundaries), grown-in macroscopic Si3N4 inclusions, and inversion layers caused by microscopic SiC precipitates on grain boundaries crossing the wafer. Copyright © 2004 John Wiley & Sons, Ltd.

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Shunt Types in Crystalline Silicon Solar Cells

We compare the dark current-voltage (IV) characteristics of three different thin-film solar cell types: hydrogenated amorphous silicon (a-Si:H) p-i-n cells, organic bulk heterojunction (BHJ) cells, and Cu(In,Ga)Se2 (CIGS) cells. All three device types exhibit a significant shunt leakage current at low forward bias (V<∼0.4) and reverse bias, which cannot be explained by the classical solar cell diode model. This parasitic shunt current exhibits non-Ohmic behavior, as opposed to the traditional constant shunt resistance model for photovoltaics. We show here that this shunt leakage (Ish), across all three solar cell types considered, is characterized by the following common phenomenological features: (a) voltage symmetry about V=0, (b) nonlinear (power law) voltage dependence, and (c) extremely weak temperature dependence. Based on this analysis, we provide a simple method of subtracting this shunt current component from the measured data and discuss its implications on dark IV parameter extraction. We propo...

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Universality of non-ohmic shunt leakage in thin-film solar cells

An experimental analysis of illumination intensity and temperature dependency of photovoltaic cell parameters

Infrared lock-in thermography allows to image shunts very sensitively in all kinds of solar cells and also to measure dark currents flowing in certain regions of the cell quantitatively. After a summary of the physical basis of lock-in thermography and its practical realization, four types of quantitative measurements are described: local I–V characteristics measured thermally up to a constant factor (LIVT); the quantitative measurement of the current through a local shunt; the evaluation of the influence of shunts on the efficiency of a cell as a function of the illumination intensity; and the mapping of the ideality factor n and the saturation current density J0 over the whole cell. The investigation of a typical multicrystalline solar cell shows that the shunts are predominantly responsible for deterioration of the low-light-level performance of the cell, and that variations of the injection current density related to crystal defects are predominantly determined by variation of J0 rather than of n. Copyright © 2003 John Wiley & Sons, Ltd.

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Quantitative evaluation of shunts in solar cells by lock-in thermography

Nine different types of shunts have been found in state of the art multicrystalline solar cells by lock-in thermography and identified by SEM-investigation (incl EBIC), TEM and EDX These shunts differ by the type of their I-V characteristic (linear or non-linear) and by their physical origin Six shunt types are process-induced, and three are caused by grown-in defects of the material The most important process-induced shunts are residues of the emitter at the edge of the cells, cracks, recombination sites at the cell edge, Schottky type shunts below grid lines, scratches, and aluminum particles at the surface The material-induced shunts are strong recombination sites at grown-in defects (eg metal-decorated small-angle grain boundaries), grown-in macroscopic SiN inclusions, and inversion layers crossing the wafer (eg carbon-induced)

Shunt types in multicrystalline solar cells

Infrared lock-in thermography not only allows one to image shunts very sensitively in all kinds of solar cells, but also to measure dark currents flowing in certain regions of the cell quantitatively. After dealing with the physical basics of quantitative lock-in thermography, three types of measurements are described: 1. the quantitative measurement of the I-V characteristic of a point shunt, 2. the evaluation of the influence of shunts on the efficiency of a cell as a function of the illumination intensity, and 3. the mapping of the ideality factor n and the saturation current density J/sub 0/ over the whole cell. The investigation of a typical multicrystalline solar cell shows that the shunts are deteriorating predominantly the low light level performance of the cell, and that crystal defect related variations of the injection current density are predominantly caused by a variation of J/sub 0/ rather than of n.

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Quantitative analysis of the influence of shunts in solar cells by means of lock-in thermography

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M.H. Al Rifai

Papers

Shunt Types in Crystalline Silicon Solar Cells

Quantitative evaluation of shunts in solar cells by lock-in thermography

Shunt types in multicrystalline solar cells

Quantitative analysis of the influence of shunts in solar cells by means of lock-in thermography

Quantitative analysis of the influence of shunts in solar cells by means of lock-in thermography