Development of Hydrogenated Silicon Sub-oxide Doped Layers and Light Trapping Structures for Enhancing Light Management in Silicon-based Thin-film Solar Cells

• Main Authors: Chen, Pei-Ling, 陳珮伶
• Other Authors: Tsai, Chuang-Chuang
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/fyp6p6

博士 === 國立交通大學 === 光電工程研究所 === 106 === We developed and characterized the hydrogenated silicon sub-oxide doped layers and light trapping structures for enhancing light managements in silicon-based thin-film solar cell. This thesis covers five main research topics: (i) development of p-type μc-SiOx:H with wide bandgap and high conductivity by optimizing deposition conditions, (ii) development of p-type SiOx:H alloy prepared in transition region with high conductivity as window layer in a-Si:H/a-Si1-yGey:H tandem cells by adjusting H2-to-SiH4 flow ratio (RH2), (iii) development of p-type and n-type μc-SiOx:H with wide bandgap, and high conductivity as p-layer of the bottom cell and back-reflecting layer (BRL) in a-Si:H/μc-Si:H tandem cells, (iv) applications of optimized p-type and n-type μc-SiOx:H as dual-functional intermediate reflection layer and tunneling recombination junction (IRL/TRJ) in a-Si:H/μc-Si1-zGez:H tandem cells, and (v) development of assembled Ag nanoparticles (Ag NPs) by chemical method and periodic SiO2 light trapping structures by nanoimprint technology in a-Si:H/a-Si1-yGey:H tandem cells. The p-type c-SiOx:H thin-films were deposited by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). By increasing RH2 and deposition pressure, the film exhibited the increased conductivity of 0.23 S/cm and the enhanced crystalline volume fraction (XC) of 43.7%. However, under higher pressure process conditions, the degraded the conductivity of 1.37×10-3 S/cm and XC of 32.7% was observed, resulting from the insufficient hydrogen etching during film growth. The p-type SiOx:H films were prepared in the transition region as a window layer in a-Si:H/a-Si1-yGey:H tandem cells. By increasing the RH2 from 10 to 167, the SiOx:H(p) remained amorphous and exhibited an increased hydrogen content. Compared to the a-SiOx:H(p) prepared at low-RH2, the SiOx:H(p) deposited at the RH2 of 167 exhibited a wide bandgap of 2.04 eV and a higher conductivity of 1.15×10-5 S/cm. With the employment of SiOx:H(p) prepared by increasing RH2 from 10 to 167 in a-Si:H cells, the FF was improved from 65 to 70% and the efficiency increased from 7.4 to 8.7%. However, the cell employed SiOx:H(p) with RH2 over 175 degraded the p/i interface and the cell performance. The a-Si:H/a-Si1-yGey:H tandem cells employing SiOx:H(p) deposited with RH2 of 167 showed an efficiency of 10.3%, with VOC of 1.60 V, JSC of 9.3 mA/cm2 and FF of 68.9%. The p-type and n-type μc-SiOx:H were prepared as doped layers of bottom cell in a-Si:H/μc-Si:H tandem cells. Regarding the doped μc-SiOx:H films, the wide optical bandgap (E04) of 2.33 eV while maintaining a high conductivity of 0.2 S/cm could be obtained with [O] of 20 at.%. Compared to the μc-Si:H(p) as window layer in μc-Si:H cells, the application of μc-SiOx:H(p) increased the VOC and led to a significant enhancement in the short-wavelength spectral response. Meanwhile, the employment of μc-SiOx:H(n) instead of conventional ITO as BRL enhanced the spectral response in the long-wavelength region. Compared to the reference cell, the optimized a-Si:H/μc-Si:H tandem cell by with p-type and n-type μc-SiOx:H exhibited an efficiency of 10.51%, which was a relative enhancement of 16%. The p-type and n-type c-SiOx:H films were prepared as functional layers in IRL/TRJ structures for a-Si:H/c-Si1-zGez:H tandem cell applications. Compared to the reference cell without the IRL/TRJ structure, the cell with µc-SiOx:H(n)/µc-Si:H(n)/µc-Si:H(p) structure as IRL/TRJ showed a significant increase in FF from 57.3 to 69.3% without the S-shaped J-V curve. Furthermore, replacing µc-Si:H(p) with µc-SiOx:H(p) increased the VOC from 1.32 to 1.35 V due to the higher E04 than µc-Si:H(p). Using the µc-SiOx:H(n)/µc-SiOx:H(p) as IRL/TRL structure in tandem cells exhibited the improved FF of 72.1% and the efficiency of 9.6%. After optimizing the CO2-to-SiH4 flow ratio (RCO2) and the thickness of µc-SiOx:H(n) IRL layer, the high efficiency of 11.6% was obtained by employing 40-nm-thick µc-SiOx:H(n) prepared at RCO2 of 1. The chemically assembled Ag NPs and the periodic SiO2 structure were developed to enhance the light management in a-Si:H/a-Si1-yGey:H tandem cells. With increasing Na3C6H5O7 concentration, the segregated Ag NPs employed in tandem cells increased spectral response in long-wavelength. In addition, as the Ag particle size increased, the increased spectral response in long-wavelength was due to the increased diffuse reflectance. However, too larger particle size than 150 nm decreased spectral response. The optimized a-Si:H/a-Si1-yGey:H tandem cell by employing Ag NPs of 150 nm prepared at Na3C6H5O7 concentration of 20 mM showed a high efficiency of 9.54%. Regarding the SiO2 structure on SnO2:F side in solar cells, with increasing the pillar height, the obviously increased spectral response was due to the increased roughness on surface. However, as the pillar height was over 200 nm, the decreased spectral response was ascribed to the remained interstitial SiO2. The optimal a-Si:H/a-Si1-yGey:H tandem cells by employing SiO2 with pillar height of 150 nm obtained an efficiency of 8.81%.