Toward High Solar Cell Efficiency with Low Material Usage: 15% Efficiency with 14 μm Polycrystalline Silicon on Glass

Abstract

Liquid‐phase‐crystallized silicon (LPC‐Si) is a bottom‐up approach to creating solar cells with the potential to avoid material loss and energy usage in wafer slicing techniques. A desired thickness of silicon (5–40 μm) is crystallized with a line‐shaped energy source, which is a laser, herein. The first part reports the efforts to optimize amorphous silicon contact layers for better surface passivation. The second part covers laser firing on the electron contact. It enables a controllable trade‐off between charge collection and fill factor (FF) by creating a low resistance contact, while preserving a‐Si:H (i) passivation in other areas. Short‐circuit current density (JSC) is observed to be up to 33:1 mA cm−2, surpassing all previously reported values for this technology. Open‐circuit voltage (VOC) of up to 658 mV also exceeded every previous value published at a low bulk doping concentration (1 × 1016 cm−3). Laser firing reduced JSC by 0:6 mA cm−2 on average but improved the FF by 22.5% absolute on average, without any significant effect on VOC. Collectively, these efforts have helped in achieving a new in‐house record efficiency for LPC‐Si of 15.1% and show a potential to reach 16% efficiency in the near future with optimization of series resistance.

Very Thin (56 μm) Silicon Heterojunction Solar Cells with an Efficiency of 23.3% and an Open‐Circuit Voltage of 754 mV

“…[4,5] Experimentally, thin (w < 100 μm) and very thin (w < 70 μm) c-Si cells have been investigated based on various technologies such as sliced/thinned free-standing wafers, [6][7][8][9][10][11] epitaxially grown Si thin layers, [12][13][14][15][16][17][18][19][20] exfoliated Si films, [19,21] Si on insulator (SOI) wafers, [22][23][24] and polycrystalline Si thin films. [25,26] The first very thin c-Si cell having η > 20% was demonstrated by Wang et al in 1996, [6] whereby a 21.5% efficient passivated emitter rear locally diffused (PERL) cell was fabricated using float-zone (FZ) Si wafers (w ¼ 47 μm) and thinned by chemical etching. Afterward, several groups developed thin c-Si cells intensively based on epitaxial lift-off technology which was suited to producing thin c-Si layers with minimal material usage.…”

“…PV properties of various c-Si solar cells as a function of c-Si wafer/absorber thickness, w: a) V OC , b) J SC , c) FF, and d) efficiency. The difference in symbol types indicates the different approaches for preparing the thin c-Si absorber and the cell architectures: standard slicing or thinning (SHJ cells[9,20,31,34,[36][37][38][39][40][55][56][57] including heteroback contacts[30,32,33,55] and other types[6,8,9,11,18,[58][59][60][61][62] ), epitaxially grown c-Si films,[12][13][14][15][16][17][18][19][20]27] SOI,[24] exfoliated Si films,[19] and polycrystalline Si films [25,26]. The filled symbols represent data for cells which have been independently confirmed.…”

Investigation of Thermal Stability Effects of Thick Hydrogenated Amorphous Silicon Precursor Layers for Liquid‐Phase Crystallized Silicon

“…Hence, EBPVD precursor layers were extensively researched for LPC solar cells and recently, a conversion efficiency of 15.1% for back‐contacted 14 μm‐thick silicon on glass was demonstrated. [ 11 ]…”

“…With regard to film thickness, we confine to films of about 4 μm, well aware that recent high efficiencies reached for this type of solar cell involved much thicker films (10–14 μm). [ 4,9,11 ] We note, however, that this type of solar cell can be fabricated with efficient light traps requiring rather thin silicon layer thickness. For example, by Green et al a silicon thickness of 1.4 μm was reported.…”

“…Hence, EBPVD precursor layers were extensively researched for LPC solar cells and recently, a conversion efficiency of 15.1% for back-contacted 14 μm-thick silicon on glass was demonstrated. [11] In the present work, we examine the thermal stability of thick PECVD-deposited a-Si:H layers on glass (coated by SiO x , SiO x / SiN y /SiO x or SiO x /SiN y /Si(O,N) x (ONO type layers) [8,9] ) under rapid annealing up to 550 C. By variation of the PECVD plasma parameters, a-Si:H material was realized that could be dehydrogenated by this rapid annealing process while other films peeled. Details of the peeling process were studied.…”