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Registration Number

0215U007714, 0115U005559 , R & D reports

Title

Ordered nanostructures on silicon surface for high efficient photovoltaic cells

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Head

Evtukh Anatoliy Antonovych,

Registration Date

25-12-2015

Organization

Institute of Semiconductor Physics of National Academy of Sciences of Ukrain

Description

Report is submitted in one volume and has 86 pages, including 42 Figures, tables 4, used sources 100. Keywords: micro- and nanostructured surfaces, silicon nanowires, metal catalytic chemical etching, electrochemical etching, porous oxide matrix. Aim: Research and development of the formation of ordered nanostructures, such as nanowires and pits on the surface of the silicon to create highly efficient photovoltaic cells. As a result of this project the following results have been obtained: 1. The technology formation of silicon nanowires by metal catalytic chemical etching has been developed. It was established that at silicon etching in a solution of HF / AgNO3 for 5 min the simple etched patterns are formed, and within 30 min - whiskers. The modification of the metal catalytic chemical etching method by different ways for mask creation allowed to obtain the regular nanoporous Si structure with an average pore diameter of the order of 700-800 nm, and randomly ordered nanoporous structure with pore diameter of 200 nm. Based on analysis of the technological features of these methods the nanostructured silicon surfaces have been obtained that are characterized by high absorption and low reflectivity. 2. During formation of silicon nanowires by electrochemical etching it was found that adding of oxidant to the electrolyte solution increases the silicon electrode potential relative to the electrolyte during the electrochemical etching by galvanic anodyzation that promotes the extraction of the holes from the silicon on oxidant ions, so it causes the more uniform etching of the surface. The roughness of por-Si films with increasing of the H2O2 concentrations from 0.97M to 2.5M is reduced almost twice (from 3.17 nm to 1.82 nm). The large pore sizes are the same, but their surface concentration is decreased. The model for calculating of the optical parameters of porous silicon films based on ellipsometric measurements has been proposed. In frame of this model it was confirmed that simultaneously with deep etching of bulk silicon there was the additional etching of the surface of already formed por-Si nanocrystals with increasing of the etching time. 3. Using the chemical vapor deposition technique in open flow system the arrays of Si nano whiskers on the silicon substrate with an average diameter of 200-600 nm has been obtained. It was established that the minimum reflectivity for Si nanowhiskers was 5% and the maximum value of the absorption coefficient was 97%. As a result, the new concept of creation of the antireflection surfaces based on Si nanowhiskers, grown by chemical vapor deposition, and nanoporous Si structures, obtained by metal catalytic chemical etching method, has been proposed. 4. The conditions for formation of the porous oxide matrix have been developed and optimized. It was established that for reproducible obtaining of dielectric alumina matrix with small dispersion of the diameter and the distance between the pores it is necessary to use multi-stages process. At the first stage the anodic oxidation in 0.3 M oxalic acid solution at voltage of 40 V and 0 °C for 2 hours is performed. Then the whole porous alumina is removed in the mixture of acids 0.2M H2CrO4 and 0.4M H3PO4 at 60 °C during 5 min. Then again, the anodization process is performed. And so on until there is a sharp decline in current. As a result the pore size of 20 - 35 nm has been obtained. The greatest ordering is achieved at the voltage of 40 V/. It improves with increasing of the first anodizing time and acid concentration. At the thickness of the film 2 microns the anodizing time was 15 minutes.

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Євтух Анатолій Антонович
Братусь Олег Леонідович
Григор'єв Антон Олександрович
Кизяк Анатолій Юрійович
Парфенюк Павло Васильович
Чудовська Галина Вікторівна