Electrical properties of n-type multicrystalline silicon for photovoltaic application—Impact of high temperature boron diffusion (original) (raw)
Amorphous silicon passivation applied to the front side boron emitter of n-type silicon solar cells
Hydrogenated amorphous silicon (a-Si:H) was used to passivated the front side boron emitter of n-type silicon solar cells. The main aspect was to investigate the parasitic absorption behavior of the a-Si:H layers on the solar cells front side with different thicknesses between 5 nm and 20 nm. Therefore planar solar cells featuring a diffused boron emitter and a diffused back surface field were fabricated. The cells reached energy conversion efficiencies up to 17.8% with an open- circuit voltage VOC of 641 mV for an a-Si:H thickness of 15 nm. Analogous processed reference cells, with an Al2O3 passivated emitter achieved an efficiency of 19% and a VOC of 658 mV.
Boron Doped SiOx Dielectrics for Bifacial n-type and p-type Silicon Solar Cells
Energy Procedia, 2015
Bifaciality offers a high potential to increase the efficiency of industrial silicon solar cells and their integration to sustainable building design. However, not enough work has been presented on doped dielectrics for bifacial solar cells. In this work we show a study on p-doped SiO x layers for bifacial solar cells. We use a non-conventional gas precursor, hexamethyldisiloxane (HMDSO) for the silicon-oxygen source, mixed with diborane as the p-type dopant and carbon-dioxide as the additional oxygen source. Our analysis reveals that layers deposited with HMDSO are thermally stable compared to the case when silane is used. Electrochemical capacitance voltage and secondary ion mass spectrometry measurements confirm the formation of a uniform boron doped layer inside the silicon bulk. Furthermore, we found that the depth of p + -n and p + -p junction can be controlled by the deposition parameters and the time of thermal diffusion. Chemical analysis shows that carbon is accumulated at the dielectric/wafer interface due to a barrier formation inside the carbon rich silicon. The p-SiO x layers can be applied on n-c-Si and p-c-Si base material as an emitter and back surface field respectively, demonstrating a feasible bifacial solar cell device.
IEEE Journal of Photovoltaics, 2013
The suitability of using a boron-rich layer (BRL) formed during boron diffusion as a gettering layer for n-type silicon solar cells is investigated. We have studied the gettering effectiveness, generation of dislocations and associated bulk lifetime degradation, and the impact of the BRL on the saturation current density, for different thickness of BRL and postoxidation conditions. Our results show that a BRL deposited using BBr 3 -based furnaces is very effective at gettering interstitial Fe, removing more than 99.9% of Fe, but that the gettered Fe is released back into the wafer when the BRL is oxidized thermally. While we have detected no significant bulk degradation due to dislocations for the diffusion conditions used, there remains a tradeoff between the gettering effect and the recombination in the boron-doped region. Although the BRL can be oxidized chemically at low temperature using boiling nitric acid without losing the gettering effect, the lowest saturation current density is obtained by means of thermal oxidation, thanks partly to a lower boron surface concentration in thermally oxidized samples.
Diffusion-free high efficiency silicon solar cells
Progress in Photovoltaics: Research and Applications, 2012
Traditional POCl 3 diffusion is performed in large diffusion furnaces heated to~850 C and takes an hour long. This may be replaced by an implant and subsequent 90-s rapid thermal annealing step (in a firing furnace) for the fabrication of p-type passivated emitter rear contacted silicon solar cells. Implantation has long been deemed a technology too expensive for fabrication of silicon solar cells, but if coupled with innovative process flows as that which is mentioned in this paper, implantation has a fighting chance. An SiOx/SiN y rear side passivated p-type wafer is implanted at the front with phosphorus. The implantation creates an inactive amorphous layer and a region of silicon full of interstitials and vacancies. The front side is then passivated using a plasma-enhanced chemical vapor deposited SiN x H y . The wafer is placed in a firing furnace to achieve dopant activation. The hydrogen-rich silicon nitride releases hydrogen that is diffused into the Si, the defect rich amorphous front side is immediately passivated by the readily available hydrogen; all the while, the amorphous silicon recrystallizes and dopants become electrically active. It is shown in this paper that the combination of this particular process flow leads to an efficient Si solar cell. Cell results on 160-mm thick, 148.25-cm 2 Cz Si wafers with the use of the proposed traditional diffusion-free process flow are up to 18.8% with a V oc of 638 mV, J sc of 38.5 mA/cm 2 , and a fill factor of 76.6%.
physica status solidi (a), 2019
Highly doped polysilicon (poly-Si) on ultra-thin oxide layers are highlighted as they allow both carrier collection efficiency with a low contact resistivity and an excellent surface passivation. Their integration at the rear surface of a highquality single-crystalline silicon solar cell allows to achieve a record conversion efficiency of 25.7% for a double-side contacted device. However, so far, only a very few studies investigate the interactions between poly-Si passivating contacts and low-quality cheaper silicon wafers. Thus, this study focuses on the external gettering response of both boron (B) and phosphorus (P) in situ doped poly-Si passivating contacts on high-performance multicrystalline silicon. Wafers are extracted from five ingot heights and experience P-and B-doped poly-Si passivating contact fabrication processes. Subsequently, the bulk carrier lifetime and interstitial iron (Fe i) concentration are characterized and compared with conventional POCl 3 and BCl 3 thermal diffusion steps, and as-cut references. The P-doped poly-Si contact fabrication process results in gettering more than 99% of the Fe i , which leads to an increase in the bulk carrier lifetime. Interestingly, the B-doped poly-Si contact also develops a substantial external gettering action, and allows removing 96% of the Fe i from the bulk.
Stability of P-I-N Amorphous Silicon Solar Cells with Boron-Doped and Undoped I-Layers
MRS Proceedings, 1985
Boron-doping the i-layer in p-i-n amorphous silicon solar cells improves the device performance when the density of impurities in the undoped i-layer material is high (< 1020 cm-3). While this technique can boost the initial device efficiencies for poor quality i-layer material, our devices degrade faster than devices made with undoped, low impurity i-layer material. We have measured the degradation of photovoltaic parameters as a function of continuous AM1 exposure time for devices with and without B-doped i-layers. For single junction p-i-n solar cells with comparable initial conversion efficiencies (< 7%, area < 1cm2) we find that our devices containing i-layers deposited from gas mixtures containing 2–3 ppm diborane degrade faster than devices containing undoped i-layers. Similar effects are observed when two-junction stacked cells with B-doped i-layers are compared to two-junction stacked cells with undoped i-layers.
Turkish journal of physics, 2011
In this work, we investigate the influence of doping as well as heat treatments on the mobility of the carriers in polycrystalline silicon layers. It was found that any increase in both parameters leads to an increase in the mobility of the carriers. Such mobilities were shown to be higher in boron doped layers that those doped with arsenic. Moreover, for strong arsenic doping, after the initial increase, we observed a saturation region followed by a final decrease of carrier mobility.
High-efficiency n-type silicon solar cells with front side boron emitter
2009
High-efficiency n-type PERL solar cells with a front side boron emitter passivated by ALD Al 2 O 3 are presented within this work. For the applied PERL cell design two variations have been employed: i) different boron emitters (deep / shallow) and ii) different dielectric layers for rear side passivation (thermal grown SiO 2 and PECVD SiN x ). Both, thermal grown SiO 2 as well as PECVD SiN x provide an effective passivation of the n-type rear surface with effective surface recombination velocities of 4 cm/s and 7 cm/s respectively. If the metalized rear side point contacts (with BSF) together with the recombination of the 1 Ω cm FZ base silicon are taken into account this results in saturation current densities of 30 fA/cm 2 and 37 fA/cm 2 respectively, limiting the open-circuit voltage (all recombination losses due to the front side are neglected) to 717 mV and 712 mV. The passivation of the boron emitter with ALD Al 2 O 3 results in an emitter saturation current density as low as 11 fA/cm 2 . Together with the losses at the rear side as well as the front side contacts this allows for an open-circuit voltage of the applied PERL solar cell design of ~700 mV. For n-type PERL solar cells featuring a lowly doped boron emitter as well as a SiO 2 passivated rear such a high open-circuit voltage (up to 703.6 mV) could be reached also at the device level, resulting in a conversion efficiency of 23.4%. Also for the PERL solar cells featuring a high surface concentration boron emitter with a PECVD SiN x passivated rear, i.e. first steps towards an industrial structure, still a high conversion efficiency of 21.8% could be achieved. All cells have been shown to be perfectly stable under illumination at 1 sun.