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[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

/pdf/diamond-like-amorphous-carbon-3pczopr0z7.pdf

Diamond-like amorphous carbon

The ionic defects at the surfaces and grain boundaries of organic–inorganic halide perovskite films are detrimental to both the efficiency and stability of perovskite solar cells. Here, we show that quaternary ammonium halides can effectively passivate ionic defects in several different types of hybrid perovskite with their negative- and positive-charged components. The efficient defect passivation reduces the charge trap density and elongates the carrier recombination lifetime, which is supported by density-function-theory calculation. The defect passivation reduces the open-circuit-voltage deficit of the p–i–n-structured device to 0.39 V, and boosts the efficiency to a certified value of 20.59 ± 0.45%. Moreover, the defect healing also significantly enhances the stability of films in ambient conditions. Our findings provide an avenue for defect passivation to further improve both the efficiency and stability of solar cells. Losses in solar cells can be caused by material defects in the bulk or at interfaces. Here, Zheng et al. use quaternary ammonium halides to passivate various perovskite absorbers and prepare solar cells with certified efficiency above 20%, suggesting that both anionic and cation defects are affected.

https://par.nsf.gov/servlets/purl/10056130

Defect passivation in hybrid perovskite solar cells using quaternary ammonium halide anions and cations

Organic photovoltaics (OPVs) evolve in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) has in the last decade been increased by almost a factor of ten approaching 10%. A main concern has been the stability that was previously measured in minutes, but can now, in favorable circumstances, exceed many thousands of hours. This astonishing achievement is the subject of this article, which reviews the developments in stability/degradation of OPVs in the last five years. This progress has been gained by several developments, such as inverted device structures of the bulk heterojunction geometry device, which allows for more stable metal electrodes, the choice of more photostable active materials, the introduction of interfacial layers, and roll-to-roll fabrication, which promises fast and cheap production methods while creating its own challenges in terms of stability.

Stability of polymer solar cells.

Light-induced metastability in hydrogenated nanocrystalline silicon (nc-Si:H) single-junction solar cells has been studied systematically under various conditions. We observe no light induced degradation when the photon energy used is smaller than the bandgap of hydrogenated amorphous silicon (a-Si:H); while degradation occurs when the photon energy is larger than the bandgap. We conclude that the light-induced defect generation occurs mainly in the amorphous phase. Contrary to a-Si:H cells, a forward current injection does not degrade the c-Si:H cell performance. However, applying a reverse bias during light soaking unexpectedly enhances the light-induced degradation.

http://ieeexplore.ieee.org/iel5/9889/31426/01488406.pdf

Study of metastability in hydrogenated nanocrystalline silicon solar cells

Excellent surface passivation of p-type TOPCon enabled by ozone-gas oxidation with a single-sided saturation current density of ∼ 4.5 fA/cm2

Characterization of tunnel oxide passivated contact with n-type poly-Si on p-type c-Si wafer substrate

We use micro-Raman and photoluminescence (PL) spectroscopy to study the effects of an a-Si:H buffer layer at the i/p interface of the mixed-phase silicon solar cells. We find that the signature of the crystalline 520 cm−1 mode still appears on the Raman spectrum for the cells with a 100 A thick a-Si:H buffer layer; but it completely disappears for cells with a 500 A thick a-Si:H buffer layer. At 80 K, the PL spectral lineshape reflects the features of the electronic states in the band tails. The characteristics of the PL spectra of the mixed-phase cells are a narrower main band than the standard a-Si:H band and an extra low energy band from the grain boundary region. As the thickness of the a-Si:H buffer layer increases, the PL main band becomes broader, and the low energy band is depressed. We find that, after light soaking, the PL main band is slightly broadened for the cells with no a-Si:H buffer layer, almost no change for the cells with a 100 A thick buffer layer, and a remarkable decrease in total PL intensity for the cells with a 500 Â thick buffer layer. In addition, the PL intensity of the defect band increases after light soaking for the cells with a 500 A thick buffer layer, where light-induced defect generation in the a-Si:H buffer layer masks the changes in the mixed-phase intrinsic layer. The Raman and PL results are consistent with previous observations of the effect of an a-Si:H buffer layer on the performance and metastability against light soaking for mixed-phase solar cells.

Buffer-layer Effect on Mixed-Phase Cells Studied by Micro-Raman and Photoluminescence Spectroscopy

A series of pure hydrogenated amorphous silicon (a-Si:H) samples as well as carbon (aSi:C:H) and sulfur alloys (a-Si:S:H) were investigated by means of the photoconductive time-of-flight technique. Drift moblility (fud) measurements reveal a fast decrease of the electron fud upon C or S addition, while the hole fud does not change significantly. Contrary to the electron transients, hole transient currents do not show the typical space-charge-limited (SCL) features, even for high light intensities where these features are normally seen. SCL features are observed to disappear for electron transients as well in the a-Si:H alloys with increasing alloy content. Above results are all explained starting from the a-Si:H density of states (DOS) model where the valence band (VB) tail is much broader than the conduction band (CB) tail. Introducing additional disorder by alloying broadens both the VB and the CB tails while the relative increase of the CB tail is much greater than that of the VB tail.

Baojie Yan

Papers

Study of metastability in hydrogenated nanocrystalline silicon solar cells

Excellent surface passivation of p-type TOPCon enabled by ozone-gas oxidation with a single-sided saturation current density of ∼ 4.5 fA/cm2

Characterization of tunnel oxide passivated contact with n-type poly-Si on p-type c-Si wafer substrate

Buffer-layer Effect on Mixed-Phase Cells Studied by Micro-Raman and Photoluminescence Spectroscopy

Electron and Hole Transient Currents in Hydrogenated Amorphous Silicon and Some Alloys Measured by the Photoconductive Time-of-Flight Technique