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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).

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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.

Principles of dopant-free electron-selective contacts based on tunnel oxide/low work-function metal stacks and their applications in heterojunction solar cells

The open-circuit voltage (Voc) of hydrogenated amorphous silicon solar cells has been studied experimentally and by computer simulation. We find that band gap and defect states affect Voc significantly. Hydrogen (H2) dilution widens the band gap and reduces density of defect states; both contribute to larger Voc and better fill factor in H2 diluted solar cells. Valence band tail narrowing could affect Voc, but is not included in this study due to lack of available data.

Effect of hydrogen dilution on the open-circuit voltage of hydrogenated amorphous silicon solar cells

Ag/ZnO back reflectors (BR) on specular stainless steel substrates are optimized for hydrogenated amorphous silicon germanium alloy (a-SiGe:H) and nanocrystalline silicon (nc-Si:H) solar cells. The BRs are deposited using a sputtering method. The texture of the Ag and ZnO layers is controlled by deposition parameters as well as chemical etching with diluted HCl. The surface morphology is investigated by atomic force microscopy. The scattered light intensity from a He-Ne laser, which illuminates the sample surface perpendicularly, is measured at different angles. Finally, a-SiGe:H and nc-Si:H solar cells are deposited on the BR substrates prepared under various conditions. For a-SiGe:H bottom cells, the improved BR with large micro-features leads to an enhanced open-circuit voltage. For the nc-Si:H solar cells, large micro-features on the improved BR eliminate interference fringes otherwise observed in the quantum efficiency measurement and result in high short circuit current density. The result is consistent with an enhanced scattered light intensity. Hence, the cell performance was improved. We also deposited a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells on the optimized BR and achieved a high initial active-area efficiency of 14.6%.

Improved Back Reflector for High Efficiency Hydrogenated Amorphous and Nanocrystalline Silicon Based Solar Cells

Optical design and optimization for back-contact perovskite solar cells

Local current flow in amorphous and nanocrystalline mixed-phase n-i-p silicon solar cells is measured using conductive atomic force microscopy (C-AFM) and correlated to the material structure from Raman measurement. The C-AFM images show that the current is very low over the entire surface of the fully amorphous region. High current spikes are observed in the mixed-phase region, where the current spike corresponds to aggregations of nanocrystallites. The size of the nanocrystalline aggregations is on the order of a half micrometer in diameter. The density of the current spike increases from the mixed phase to the heavily nanocrystalline regions. A thick amorphous silicon buffer layer inserted between the p and i layers significantly reduced the magnitude of the current spike. The C-AFM measurements suggest that the mixed-phase cells can be considered as a two-phase parallel-connected diode structure, consistent with our previously proposed model.

Baojie Yan

Papers

Principles of dopant-free electron-selective contacts based on tunnel oxide/low work-function metal stacks and their applications in heterojunction solar cells

Effect of hydrogen dilution on the open-circuit voltage of hydrogenated amorphous silicon solar cells

Improved Back Reflector for High Efficiency Hydrogenated Amorphous and Nanocrystalline Silicon Based Solar Cells

Optical design and optimization for back-contact perovskite solar cells

Local current flow in amorphous and nanocrystalline mixed-phase silicon solar cells