Optical properties and impedance spectroscopy analyses for microscale Si pillar solar cells

In this data article, optical properties and impedance spectroscopy analyses were applied for the 5 μm-height pillar Si solar cells to analyzed the insight of the Si geometric effect (Yadav et al., 2017) [1]. The surface reflectance data measured for all Si pillar samples (Fixed height of 5 μm with varying width and period. Geometric features of Si pillars are summarized in Table 1) are presented. Statistical data after analysis are summarized in the table, to profile the integrated reflectance quantitatively. Impedance spectroscopy analyses of all the samples were performed to demonstrate the bias-dependent space charge region. Mott–Schottky investigation shows the enhancement of built-in potential values due to the pillar structures.


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In this data article, optical properties and impedance spectroscopy analyses were applied for the 5 μm-height pillar Si solar cells to analyzed the insight of the Si geometric effect (Yadav et al., 2017) [1]. The surface reflectance data measured for all Si pillar samples (Fixed height of 5 μm with varying width and period. Geometric features of Si pillars are summarized in Table 1) are presented. Statistical data after analysis are summarized in the table, to profile the integrated reflectance quantitatively. Impedance spectroscopy analyses of all the samples were performed to demonstrate the bias-dependent space charge region. Mott-Schottky investigation shows the enhancement of built-in potential values due to the pillar structures.
& 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Subject area
Physics, Electrical Engineering More specific subject area

Solar cells
Type of data Figures, Table  How

Value of the data
Area under the curve of reflectance of the Si microscale pillar solar cells would be useful to estimate the overall reflectance quantitatively; this analysis could be applicable to efficient anti reflectance coating researches.
The bias dependent impedance spectra revealed the functional modulation of the space charge region of Si pillar solar cells.
The Mott-Schottky measurement demonstrates the enhanced built-in potential according to the pillar structures.
1. Data Fig. 1 shows surface reflectance of various microstructured Si solar cell, recorded by diffused integrated sphere UV-visible spectrophotometer. Microstructure Si samples are well detailed in our report [1]. Table 1 shows the integrated area under the curve of reflectance profiles. Impedance spectra of the reference flat Si device and champion pillar-1 device are shown in Fig. 2. Impedance spectra of the pillar Si devices are shown in Fig. 3. Impedance spectra of all the devices are shown for forward and reverse bias dark conditions. The Mott-Schottky characteristics of all the samples are shown in Fig. 4.

Sample preparation
The 500 µm thick p-type (100) Si wafer (Czochralski) was used as a base substrate. To form the microscale pillar structures, the photolithography mask patterns were previously formed on the Si substrate, which serve as the etching mask during the Si etching process. The exposed Si region is going to etch away. For the reactive etching, SF 6 -plasma was employed for several loops for 10 min to etch the residual polymer layer and the exposed Si parts without the PR masks. Table 1 Parameters of 5 μm scale Si pillar structures. Summary of integrated area under the curve of reflectance spectra, as shown in Fig. 1.

Sample
Area under the curve¼∫ 1100nm 350nm R λ ð Þdλ Flat Si 7921.9 Pillar 1 (width ¼ 2 μm, period ¼4 μm, depth¼ 5 μm) 4986.0 Pillar 2 (width ¼ 2 μm, period ¼7 μm, depth¼ 5 μm) 4500.7 Pillar 3 (width ¼ 5 μm, period ¼7 μm, depth¼ 5 μm) 3645.6 Pillar 4 (width ¼ 5 μm, period ¼10 μm, depth¼5 μm) 4810.6 For the formation of a p-n junction, n-type doping was done using phosphorous oxy-chloride (POCl3) source. After the formation of the n-type layer, a buffered hydrofluoric acid (5% HF) solution was used to remove the phosphosilicate glass (PSG). A thin 80 nm SiNx layer was formed over n-type layer, which actively acts as an antireflection coating and passivating layer. The size of the samples was 3.2×3.2 cm 2 which is among one of the most efficient micro-structured solar cell with this area. The metal contacts were formed by screen printing the silver (Ag) and aluminium (Al) paste at front and back contacts, respectively, before co-firing. Planar cells with the same area but without any micro-structures were used to produce a planar junction device for the performance comparison [1].

Sample characterizations
Reflectance data for the fabricated samples between the wavelength ranges from 300 nm to 1100 nm are presented in Fig. 1. An integrated sphere attachment supplied with UV-vis spectrophotometer (Shimadzu-2600) was used for carrying out the diffused reflectance measurements. A necessary baseline correction was done prior to recording the reflectance spectra by using BaSO 4 pallets. The area under the curve of reflectance profiles shown by Gray solid region is summarized in Table 1. The area under the curve was estimated over the photon wavelength range 350 nm (lower limit) to 1100 nm (upper limit). Integration function was applied for summing the finite region of interval 1 nm.
Impedance spectra of the planar and the Pillar 1 device are presented in Fig. 2. These data were measured in the dark condition for the forward bias and reverse bias conditions. The cole-cole plots for reverse bias (left) and forward bias (right) of the flat and pillar-1 devices are shown discretely. These data were recorded for the applied bias range from −0.7 V to 0.4 V with an interval of 0.1 V. These measurements were performed over the frequency range from 1 MHz to 1 Hz. Fig. 3 shows the cole-cole plots recorded for the Pillar-2, pillar-3 and pillar-4 devices. These plot shows the relation of real impedance (Z') vs imaginary impedance (Z").
Mott-Schottky characteristics (1/C 2 -V characteristics) obtained by using the Potentiostat/Galvanostat (ZIVE SP1, WonA Tech, Korea) is shown in Fig. 4. The Potentiostat/Galvanostat was calibrated with a standard static and dynamic circuit before the impedance and Mott-Schottky measurement. The MS measurements were performed at 20 kHz of frequency.