Development of industrial processes for the fabrication of high efficiency n-type PERT cells

Industrial bifacial n‐type front and back contact (nFAB) silicon solar cells, consisting of a boron‐doped p+ emitter and a phosphorus‐doped n+ back surface field (BSF), are known to give good bifaciality, high and stabilized efficiency. One possible approach to further enhance the cell efficiency is to convert conventional passivated emitter and rear totally diffused (PERT) into rear locally diffused (PERL) structure. Herein, bifacial nFAB PERT and PERL cells are fabricated by combining atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG) as doping source and laser processing. For PERL cells, two approaches are studied to locally form phosphorus‐doped BSF: 1) laser doping, and 2) laser ablation of a diffusion barrier layer. For ablation approach, an alkaline treatment is introduced immediately after laser process, which leads to the formation of locally textured BSF. Due to this locally textured contact, the resultant fill factor (FF) and series resistance (Rs) loss of the PERL cells are even less than that of the reference PERT cells. As a result, the champion cell of PERL shows a good efficiency of 21.3% with open‐circuit voltage (Voc) of 662 mV, short‐circuit current density (Jsc) of 39.6 mA cm−2, and a high FF of 81.1%.

Section: Introductionmentioning

confidence: 99%

Development of High‐Efficiency n‐Type Front and Back Contact Passivated Emitter and Rear Locally Diffused Solar Cells Using Atmospheric Pressure Chemical Vapor Deposition of Phosphosilicate Glass and Laser Processing

Yan

Ning

Suhaimi

et al. 2020

“…The POCl 3 diffusion is a two‐sided process that diffuses both (unprotected) wafer sides. Thus, a protection layer is needed . Ion implantation and CVD can be applied single‐sided.…”

Section: Introductionmentioning

confidence: 99%

Development of Bifacial n‐Type Front‐and‐Back Contact Cells with Phosphorus Back Surface Field via Mask‐Free Approaches

Ning

Wang

Yan

et al. 2019

Industrial bifacial n-type front-and-back contact (nFAB) solar cells consist of a boron-doped p þ emitter and a phosphorus-doped n þ back surface field (BSF). A conventional BSF formation method with tube-based POCl 3 diffusion typically requires the use of a masking layer to protect the front emitter against cross doping or two wet-chemical etching steps. Herein, two alternative mask-free BSF formation approaches are investigated, either via phosphorus ion implantation or atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG). The fabricated cells indicate comparable efficiencies achievable by mask-free methods, as compared with conventional tube-based POCl 3 diffusion. In addition, the APCVD process is further improved by optimizing the phosphorus contents in the PSG layer. Cell performances with different phosphorus contents and thus different BSF sheet resistances are studied. A lower phosphorus content (higher BSF's sheet resistance) improves cells' J sc , whereas a higher phosphorous content results in high fill factor (FF) due to better rear contact resistance and low BSF sheet resistance. The optimized condition results in nFAB cell with a peak efficiency of 21.4% and FF values over 81.0%.

“…Conventionally, boron doped SiO x layers (borosilicate glass, BSG) and phosphorous doped SiO x layers (phosphorous silicate glass, PSG) are deposited with silicon (and oxygen) precursors such as silane (SiH 4 ) , tetramethoxysilane (TMOS) , tetraethylorthosilicate (TEOS) , hexamethyldisilazane (HMDS) , tetramethylsilane (TMS) with an additional oxygen (O) source such as oxygen (O 2 ) , ozone (O 3 ), nitrous oxide (N 2 O) , or carbon dioxide (CO 2 ) . The doping of the silicate glass is done by including B 2 H 6 , trimethylboron or BBr 3 (p‐type dopants) or PH 3 , POCl 3 (n‐type dopants) in the gas mixture.…”

Section: Introductionmentioning

confidence: 99%

Analysis of p‐type SiO_x layers as a boron diffusion source for n‐type c‐Si substrates

Goyal

Urrejola

Hong

et al. 2016

We evaluate the use of p‐type silicon oxide (p‐SiOx) dielectric layers as a boron diffusion source for n‐type crystalline silicon (c‐Si) substrates. The p‐SiOx layers grown on n‐type c‐Si substrates by plasma enhanced chemical vapor deposition using a gas mixture of He/hexamethyldisiloxane/CO2/B2H6 are thermally stable and do not peel off during annealing up to 1050 °C, making them effective diffusion sources. The layers were examined before and after annealing with characterization techniques including spectroscopic ellipsometry and secondary ion mass spectrometry. We observe that there is a reduction in the thickness of the p‐SiOx layer after annealing by about 50%, and that boron diffuses into the n‐type c‐Si substrate, forming a p+ layer, limited by the formation of a carbon‐rich layer above the c‐Si surface. The concentration of holes in the diffused region was measured by the electrochemical capacitance–voltage technique, and it was found that essentially all the boron that diffused into the n‐type c‐Si was active, unaffected by the presence of carbon and oxygen atoms. The concentration of carriers can be controlled by the initial thickness of the p‐SiOx layers and the depth of the p+/n junction can be controlled by the time of annealing. A surface carrier concentration of 3 × 1019 at cm−3 and a sheet resistance of the order of 120 Ω sq−1 was obtained upon annealing at 1050 °C for 30 min.