Improvement of Conversion Efficiency of Silicon Solar Cells by Submicron‐Textured Rear Reflector Obtained by Metal‐Assisted Chemical Etching

Abstract

A 19.8% conversion efficiency has been achieved by formation of a nanocrystalline Si layer on the front surface and a submicron-textured reflector on the rear surface of monocrystalline Si solar cells. The nanocrystalline Si layer with a thickness of $200 nm formed by the surface structure chemical transfer (SSCT) method significantly decreases the front surface reflectance to less than 3%, while the submicron-textured rear surface formed by the metal-assisted chemical etching (MACE) method enhances light absorption inside Si. Both the reaction rates of the SSCT and MACE methods do not depend on crystal orientations, and therefore, these methods are applicable to polycrystalline Si solar cells. Reflectance spectra in the wavelength region longer than 950 nm of the nanocrystalline Si layer/Si structure show that the submicron-textured reflector has excellent light trapping effect equivalent to the pyramidal textured reflector. Due to this light trapping effect, the short-circuit photocurrent density of the nanocrystalline Si solar cells has been improved to 41.6 mA cm À2 .Black Si can achieve ultralow reflectance surfaces in wide wavelength and angle regions, and its application to solar cells can avoid formation of anti-reflection coating produced by use of expensive vacuum equipments such as plasma-enhanced chemical vaper deposition (PECVD). [1][2][3][4][5] Therefore, black Si solar cells can increase the light absorption probability and decrease the cell production cost. The ultralow reflectance of black Si results from formation of surface structures much smaller than the wavelength of incident light, in which the refractive index of the structure gradually changes with the depth from the surface.We have developed a simple method to produce black Si, i.e., the surface structure chemical transfer (SSCT) method, in which Si wafers immersed in an HF plus H 2 O 2 solution are just contacted with a Pt catalyst. [6] By the SSCT treatment for 15 s, a $200 nm-thick nanocrystalline Si layer with graded refractive index is formed on a Si surface, leading to an ultralow reflectance less than 3% in the wide wavelength region between 300 and 900 nm. However, the formation of the nanocrystalline Si layer greatly increases the surface area, similar to the case of other black Si structures such as nanocone, [7] nanowire [8,9] and porous Si, [10][11][12][13][14] which increases surface recombination rates. In order to suppress the surface recombination rates, we have developed an effective passivation method for the nanocrystalline Si layer, i.e., phosphosilicate glass (PSG) deposition plus heat treatment, and the internal quantum efficiency for short-wavelength light is greatly improved. [15][16][17] After the surface passivation processes, the nanocrystalline Si layer/Si solar cells generate a high shortcircuit photocurrent density ( J sc ) of 41.0 mA cm À2 even without anti-reflection coating, and the conversion efficiency of 19.5% has been achieved. [17] In the present study, we have developed a fabrication method to form ...

Communication—Enhancement of Boron Back-Surface-Field and Suppression of Auger Recombination to Improve Ultralow-Reflectance Si Solar Cells

“…Sample evaluation and solar cell fabrication were performed using the same methods reported in our previous literature. [9][10][11][12]…”

“…1). [9][10][11][12] In the SSCT method, an Si surface dissolves nonuniformly, leading to formation of a nanocrystalline Si (nc-Si) layer. The porosity of the nc-Si layer gradually decreases with the depth, and the refractive index gradually increases with it, leading to ultralow-reflectance less than ∼3% in the wide wavelength region between 400 and 900 nm.…”

Black silicon – correlation between microstructure and Raman scattering

“…In the present study the nanocrystalline Si layers were formed by using the surface structure chemical transfer method (SSCT) [8][9][10][11]. In this procedure silicon surface is etched in solution of H 2 O 2 and HF.…”

“…Self-similarity property of formed particles causes importance of fractal properties of resulting structure. This kind of structure show very low spectral reflectance in wide range of wavelengths [8][9][10][11].…”

One Sunny Year of Solar RRL: Looking Back and Gazing Ahead

“…So what could be a better way to judge the success of this young journal than by looking at our 2017 champions in terms of authors and their topics? We've made nominations in several categories: ‐ Article download champion : Light Illumination Induced Photoluminescence Enhancement and Quenching in Lead Halide Perovskite , by Xiaoming Wen, Martin Green, Anita Ho‐Baillie (University of New South Wales, Sydney) et al This inaugural contribution to the very first issue obviously had the longest viewing time − 4 times a day on average since publication. ‐ Altmetrics champion: Improvement of Conversion Efficiency of Silicon Solar Cells by Submicron‐Textured Rear Reflector Obtained by Metal‐Assisted Chemical Etching , by Daichi Irishika, Hikaru Kobayashi (Osaka University) et al This Communication is currently showing a score of 61 at wiley.altmetric.com since it was picked up by several news outlets and social networks, boosting it to the top 5% of all research outputs currently on Altmetric. ‐ Citation champion: Despite it being a bit early for citations, the recently published article High‐Performance Non‐Fullerene Polymer Solar Cells Based on Fluorine Substituted Wide Bandgap Copolymers without Extra Treatments by Xia Guo, Maojie Zhang et al (Soochow University, Suzhou) has already picked up 14 citations on Wiley Online Library to date. ‐ Efficiency champion : Although this does not necessarily mean to be a record in absolute numbers, the Letter High Efficiency Solar Cell Based on Full PVD Processed Cu(In,Ga)Se 2 /CdIn 2 S 4 Heterojunction by Nicolas Barreau (Université de Nantes) and 24 co‐authors is our first Efficiency Update article in Solar RRL . We certainly look forward to receiving more of such contributions, so please send us your latest progress in efficiencies, whether in photovoltaics, photocatalysis or others. ‐ Review champion : Recent Progress in Photocatalytic CO 2 Reduction over Perovskite Oxides by Run Shi, Tierui Zhang (Chinese Academy of Sciences, Beijing) et al is currently among the hottest Review articles in the journal and covers a major focus topic of Solar RRL , one that we wish to further strengthen in 2018. …”