Electrical properties of n-type multicrystalline silicon for photovoltaic application—Impact of high temperature boron diffusion (original) (raw)
Related papers
2005
The shortage of the p-type silicon (Si) feedstock and the high minority carrier lifetimes in multicrystalline (mc) n-type Si reported by different authors ([1]-[3]) make n-type mc-Si solar cell fabrication more and more interesting. Given the high electronic quality of the material – that is confirmed in our studies again – the task remains to develop an adapted solar cell process. A key feature of the concept presented here is the BBr3diffused emitter on the front side and the surface passivation of this emitter. We show that BBr3 emitter-diffusion is possible without degradation of the high initial carrier lifetimes in the n-type mc-Si material on contrary the diffusion even improves the average lifetime to a large extend. SiO2 provides an excellent surface passivation of the p-Si surface. Application of PECVD SiNx resulted in a decrease of the (implied) Voc measured on lifetime teststructures as well as on solar cell level. As an alternative, a low temperature surface passivation...
Energy Procedia, 2013
In this paper we investigate the material quality of n-and p-type multicrystalline silicon wafers after different hightemperature steps, as applied during cell processing. Both materials start with a high initial bulk diffusion length of around 440 μm (harmonic mean of the whole wafer) which is further improved by the solar cell process. A diffusion length of 510 μm was measured after phosphorus and boron diffusion and firing in the n-type material. The p-type wafers showed diffusion lengths of 540 μm after phosphorus diffusion and firing. These diffusion lengths were measured at a generation rate of 1/20 sun close to maximum power point injection conditions of a solar cell. At higher injection levels both materials reach 600 μm diffusion length. The high material quality of n-type material maintained after the high temperature boron diffusion is remarkable. An efficiency analysis shows that these excellent diffusion lengths allow for high efficiency devices exceeding 20% efficiency.
EFFECT OF PHOSPHOROUS/BORON DOPING PROFILE DIFFERENCES ON THE PERFORMANCE OF SILICON SOLAR CELLS
EFFECT OF PHOSPHOROUS/BORON DOPING PROFILE DIFFERENCES ON THE PERFORMANCE OF SILICON SOLAR CELLS, 2020
This research work was done under title "Effect of phosphorous/boron doping profile differences on the performance of silicon solar cells". Emitter diffusion either phosphorous or boron is quite challenging in photovoltaic industry. It directly affects the emitter saturation current density and the emitter quantum efficiency of silicon solar cells. Our main objective was to make the comparison of both phosphorous and boron diffused emitters for different peak dopant concentrations in silicon solar cells. It was done by using EDNA 2 simulations. We used different parameters in EDNA 2 and simulated the high efficiency solar cells with boron as back ground and phosphorous as emitter. Then we simulated the solar cells with phosphorous as back ground and boron as emitter. We varied the peak dopant concentration of phosphorous as well boron from 1.6E+17 to 3.9E+20. The best internal quantum efficiency of emitter for phosphorous diffused emitters was 95.1 %, obtained at 1.6E19 (cm-3) with an effective emitter depth of 0.675 (µm). However, the best internal quantum efficiency of emitter for boron diffused emitters was 80.6 %, obtained at 3.9E19 (cm-3). It has an effective emitter depth of 0.732 (µm) that is greater than obtained from phosphorous diffused emitters. We concluded that the phosphorous diffused emitters have much better performance than boron diffused emitter in silicon solar cells. They have better internal quantum efficiency of emitters at lower peak dopant concentration. They have lower emitter sheet resistance with lower effective emitter depth, as also required during silicon solar cell fabrication.
Electrical properties of boron, phosphorus and gallium co-doped silicon
Energy Procedia, 2011
A number of ingots were grown from solar grade poly Silicon, to which Boron, Phosphorous and Gallium were added as dopants. The introduction of Gallium as a third dopant allowed for a better control of the resistivity and the doping type during ingot growth. Measured resistivity in this material is shown to be systematically higher than that calculated using Scheil's law for the dopants distribution and Klaassen's model for the majority carrier mobility. This resistivity underestimation is shown to be, at least partially, due to a reduction of the majority carrier mobility in highly compensated Si compared to Klaassen's model. A similar reduction is observed for the minority carrier mobility. We propose a correction term in the mobility calculation, to allow a greater accuracy in the prediction of the resistivity and mobility of compensated solar grade silicon.
N-type multicrystalline silicon solar cells with BBr3-diffused front junction
2005
A simplified laboratory process with one photolithographic step for front junction solar cells on ntype multicrystalline (mc) silicon has been developed. The emitter diffusion is done in an open tube furnace with BBr3 and back-surface-field diffusion using POCl3, loading the wafers front-to-front and back-to-back respectively and thus avoiding additional etching steps. The front surface has been passivated by a 10 nm thermal oxide grown in a tube furnace. With this simple process, efficiencies of 11.0% on n-type mc-Si and 11.5% on n-type Cz-Si have been realized without antireflection coating and without surface texture. Applying a double layer antireflection coating (DARC) on these cells, efficiencies of 16.4% on Cz-Si and 14.7% on mc-Si have been achieved.
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.