Boron Diffusion Process Research Articles

High-efficiency n-TOPCon cells ensured by an emitter preparation process without post-oxidation

Laser-enhanced contact optimisation (LECO) technology can effectively improve the efficiency of tunnel oxide passivated contact (n-TOPCon) solar cells. Generally, the preparation of an emitter in TOPCon cells requires post-oxidation treatment at temperatures exceeding 1030 °C for over 3000 s. This high-temperature post-oxidation process results in reduced surface doping concentration, increased reflectivity of the front of the cell and elevated manufacturing costs of the junction. In this study, through process research, we reveal that the optimal profile depth of emitter (the boron doping concentration at 1 × 1018 atoms/cm3) for mass-produced LECO pastes ranges from 0.44 to 0.52 μm. Additionally, it was discovered that a boron-rich layer (BRL) thinner than 10 nm does not reduce bulk lifetime and increase contact resistivity. Based on these findings, we developed a boron-diffusion method without post-oxidation, which involves controlling the BRL thickness by adjusting the pre-oxidation layer thickness and cycle deposition. When applied to the mass production of n-TOPCon solar cells, this approach resulted in a solar cell conversion efficiency of 26.28 %. This represents an improvement of 0.03 %–0.05 % over traditional boron-diffusion processes. Furthermore, eliminating post-oxidation significantly improved the production capacity and lifespan of the boron-diffusion furnace, thereby reducing the manufacturing costs associated with the solar cells. Furthermore, eliminating post-oxidation significantly improved the production capacity and lifespan of the boron-diffusion furnace, thereby reducing the manufacturing costs associated with the solar cells.

Distribution of impurities in base-depleted region of diode temperature sensor

The performance of diode temperature sensors depends on their base-depleted region thickness and impurity distribution profile. In this article, we study the boron diffusion process in the thin base region with a thickness of about 1 μm. We show that, for the proposed p+–n–p temperature sensor structure, the impurity distribution in the n region has the form of an asymmetric parabola, with an extreme concentration point shifted towards the “upper” p+ region.

Optimization of boron depletion for boron-doped emitter of N-type TOPCon solar cells

During the preparation of boron-doped emitters for TOPCon solar cells, boron atoms accumulate, forming a boron-rich layer (BRL). Oxidation, during the boron diffusion process, can eliminate the BRL. Prolonged oxidation which forms a SiO2 layer can remove the BRL, also act as a protective mask for the front surface. Nevertheless, during high-temperature thermal oxidation, boron will be redistributed. Boron reaches a higher equilibrium concentration in SiO2 than in the silicon wafer, and the SiO2/Si interface shifts inward during SiO2 formation. Simultaneously, the high temperature during oxidation prompts the boron inside the silicon wafer to diffuse deeper. The dual effects of oxidation and diffusion cause boron to be depleted near the surface of the silicon wafer. Boron depletion leads to a reverse bending of the energy band, which hampers carrier collection and impedes further enhancement of cell power conversion efficiency. In this paper, the oxidation process was mainly adjusted to reduce surface boron depletion, resulting in approximately 0.09%abs. increase in power conversion efficiency compared to pre-optimization.

High-efficiency TOPCon solar cell with superior P + and P++ layer via one-step processing

The boron diffusion process in the front field of N-type tunnel oxide passivated contact (TOPCon) solar cells is crucial for PN junction formation and the creation of a selective emitter. This study presents a theoretical model of boron diffusion in silicon using molecular dynamics. The research examines the mean square displacement and diffusion coefficient of boron atoms at varying temperatures, confirming their diffusion behavior. The simulations indicate predominant boron diffusion in the z-direction within the silicon matrix, with the diffusion depth being temperature dependent. The optimal temperature range for boron diffusion in silicon is identified as 950 °C to 1050 °C. Using boron-doped silicon paste and boron trichloride as dopants, thermal diffusion experiments were conducted to fabricate the front-field PN junction (p+ layer) and selective emitter (p++ layer) by one step. Subsequent processing and performance evaluation were performed on a production line. Experimental findings reveal a decrease in boron diffusion at higher temperatures, reduced sheet resistance, increased doping concentration, and deeper junction formation. The ideal boron concentration in the p+ layer is 8.68 × 1018 atom/cm3 with a depth of 0.53 μm, while the p++ layer is 2.35 × 1019 atom/cm3 and 0.82 μm. The efficiency of the optimized TOPCon + cell production line reaches up to 25.17 %, marking an improvement of 0.23 % over the standard cell production line. This research contributes to elucidating the mechanism of boron diffusion and offers insights for enhancing the efficiency of TOPCon solar cells.

"Analytical Modelling of the Boron Diffusion and Etching Process for the Accurate Design and Fabrication by Bulk Micromachining Technology of the Silicon Capacitive Pressure Sensors for Biomedical Applications"

"Analytical Modelling of the Boron Diffusion and Etching Process for the Accurate Design and Fabrication by Bulk Micromachining Technology of the Silicon Capacitive Pressure Sensors for Biomedical Applications"

High-efficiency black silicon tunnel oxide passivated contact solar cells achieved by adjusting the boron diffusion process

High-efficiency black silicon tunnel oxide passivated contact solar cells achieved by adjusting the boron diffusion process

Study on the cleaning process of n+-poly-Si wraparound removal of TOPCon solar cells

The use of tunnel oxide passivated contact (TOPCon) solar cells on the n-type Cz-Si wafers has thus far attracted more interest in the photovoltaics (PV) industry. However, the cells encounter the problems of wraparound appearance and edge leakage current. These phenomena can result in the decrease in the optical and electrical performance of the cells, such as open circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF). In this work, several cleaning processes were adopted to resolve the problems for cells. The wraparound model and experimental results indicated that an effective cleaning process was carried out and revealed the correlation between the removal of the wraparound film and the edge junction layer on the surface of wafers. The optimized cleaning process did not destroy the boron-doping layer on the front side, and the poly-Si layer on the rear side. This process combined an inline etching process of HF/HNO3 treatment and a batch-type etching process of the KOH/polish additives solution treatment, which could effectively solve the problems associated with optical properties and achieve a low reversed-biased junction leakage current (IRev) 0.15 A at −14.5 V. After optimization of the rear surface recombination and the boron diffusion processes, industrial-type TOPCon cells at the present pilot line were obtained with the efficiency (Eff), Voc, Jsc and FF of 23.53%, 706 mV, 40.65 mA/cm2 and 82.02%, respectively. This optimized cleaning process could be applied and promoted in the PV industry.

Green-laser-doped selective emitters with separate BBr3 diffusion processes for high-efficiency n-type silicon solar cells

Laser-doped boron selective emitters are an ideal candidate for enabling less emitter recombination, lower contact resistance and better blue response of efficient n-type silicon solar cells. However, the low boron concentration of the borosilicate glasses formed during boron diffusion processes and the implementation of ultraviolet lasers have hindered the commercialization of laser-doped boron selective emitters. In this contribution, separate BBr3 diffusion processes for green-laser-doped selective emitters are demonstrated. Laser doping processes were conducted between (1) borosilicate glass deposition and boron driving in and (2) post-oxidation, achieving the optimized laser doped selective emitter with the Rsheet,p+/Rsheet,p++ of 95.0 Ω/□/54.3 Ω/□, accompanying with the p+ profile of Nmax < 1.4× 1019 cm−3. By comparison to the homogeneous emitter with sheet resistance of 88.9 Ω/□, J0e, total of 45.3 fA/cm2 and ρc, metal of 2.9 mΩ/cm2, the employment of the optimum laser doped selective emitter has resulted in the J0e, total of 31.1 fA/cm2 and the ρc, metal of 1.0 mΩ/cm2. Finally, the improvement of simulated VOC (699.6 mV), FF (81.38%) and efficiency (23.13%) were obtained by using the optimized laser doped SEs, compared with the simulated VOC (694.5 mV), FF (81.14%) and efficiency (22.89%) of the reference. Separate BBr3 diffusion processes for green-laser-doped selective emitters demonstrate the employment of industrial green laser and boron diffusion furnace, instead of expensive ultraviolet laser and other complex boron resources, indicating a promising potential for industrial feasibility.

Development and validation of boron diffusion model in nuclear reactor core subchannel analysis

The diffusion characteristic of borated water in nuclear reactor core is important for the reactivity control during some possible reactivity transient scenarios. The non-uniform distributions of boron concentration increase the risk of reactor accidents and lead to some reactor safety problems. Hence it is necessary to develop an effective boron diffusion model into the reactor thermal-hydraulic analysis code. In this paper, a quasi-three dimensional boron tracking model, in which the turbulent diffusion effect was considered carefully, was proposed and successfully implemented in the subchannel analysis code. The reliable CFD method with k-omega turbulent model validated against International Standard Problem (ISP No. 43) experimental data was used to verify the feasibility of proposed boron tracking model. A typical Pressurized Water Reactor (PWR) 3 × 3 fuel bundle model was established and the borated water was injected into one specified channel and pure water into other channels. The distributions and variations of boron concentration along the flow direction were achieved and analyzed. Results indicate that the proposed boron tracking model could predict the boron diffusion process in the fuel rod bundles more accurately compared with the original model. This work provides an essential supplement for the nuclear reactor subchannel analysis method.

Avoidance of boron rich layer formation in the industrial boron spin-on dopant diffused n-type silicon solar cell without additional oxidation process

In the present work, the properties of boron rich layer (BRL) formed in the boron spin-on dopant diffusion as well as the avoidance of BRL formation without additional oxidation process are studied. The boron concentration distributions characterized by SIMS exhibit the formation and avoidance of BRL with the variation of oxygen content in the boron diffusion process. The existence of BRL can degrade the minority carrier lifetime due to the enhancement of recombination as well as weaken the anti-reflection effect due to the unmatched refractive index of BRL and SiO2/SiNx stack layers. The decreased minority carrier lifetime together with the increased surface reflectance eventually deteriorates the electrical behavior of solar cell with a maximum power conversion efficiency loss of 0.55%. Significantly, the formation of BRL is found to be avoided due to the complete oxidation of excess elemental boron atoms when the oxygen content increases to 10%, contributing to the recovery of solar cells’ electrical performance with an average efficiency of 19.47%. The present work will be helpful to deepen the understanding of BRL and simplify the boron diffusion process for massive cell production.

Performance of p+ layer formed by B diffusion using boron paper

This paper presents a novel boron diffusion process using boron paper as the boron source to form a p+ layer. It was found that sheet resistance was invariable with changing the distance between boron paper and Si wafers, and diffusion uniformity was the best at a distance of 0.3 cm. Sheet resistance (Rs) decreased with increasing diffusion temperature, showing a value of 6.9 Ω/□ at 1050 °C with a high diffusion uniformity of 99.173%. The junction depth increased from 195 nm to 517 nm with diffusion temperature raised from 900 °C to 1050 °C. The influence of diffusion time on the performance of B diffusion from boron paper was similar with that of temperature.

Impact of Channel Mobility Improvement Using Boron Diffusion on Different Power MOSFETs Voltage Classes

SiC planar VDMOS of three voltages ratings (1.7kV, 3.3kV and 4.5kV) have been fabricated using a Boron diffusion process into the thermal gate oxide for improving the SiO2/SiC interface quality. Experimental results show a remarkable increase of the effective channel mobility which increases the device current capability, especially at room temperatures. At high temperatures, the impact of the Boron treatment is lower since the major contribution of the drift layer to the on-resistance. In addition, the intrinsic body diode characteristics approximate to that of an ideal PiN diode, and the blocking capability is not compromised by the use of Boron for the gate oxide formation.

Over 21% Efficiency of n-Type Monocrystalline Silicon PERT Photovoltaic Cell With Boron Emitter

We have developed an n-type monocrystalline silicon photovoltaic cell achieving the conversion efficiency of 21.3% by passivated emitter and rear totally diffused structure with a total area of 239 cm2. The center area of the cell showed 21.7% (226.3 cm2). The main developments for the cell related to an emitter are a boron diffusion process and a passivation process of the boron layer. The developed cells contain a deeply diffused and lightly doped boron emitter with a high-quality surface passivation layer to obtain high efficiency. An atmospheric pressure chemical vapor deposition (APCVD) process is used for the fabrication of a boron emitter. This process is suitable for mass production lines. An atomic layer deposition Al2O3 layer is applied for a passivation of the boron layer. In addition, the ohmic contacts between the cell and electrodes are improved by changing a temperature profile for an electrode firing process.

Characterization of Boron Diffusion Phenomena According to the Specific Resistivity of N-Type Si Wafer

This paper is directed to characterize the boron diffusion process according to the specific resistivity of the Si wafer. N-type Si wafers were used with the specific resistivity of 0.5-3.2 omega-cm, 1.0-6.5 omega-cm and 2.0-8.0 omega-cm. The boron tribromide (BBr3) was used as boron source to create the PN junction on N-type Si wafer. The boron diffusion in N-type Si wafer was characterized by sheet resistance of wafer surface, secondary ion mass spectroscopy measurements (SIMS) and surface life time analysis. The degree of boron diffusion was depended on the variation in specific resistivity and sheet resistance of the bare N-type Si wafer. The boron diffused N-Si wafer exhibited the average junction depth of 750 nm and boron concentration of 1 x 10(19). N-type Si wafer with the different specific resistance considerably affected the boron diffusion length and life time of Si wafer. It was found that the lifetime of boron diffused wafer was proportional to the sheet resistance and resistivity. However, optimization process may necessary to achieve the high efficiency through the high sheet resistance wafer, because the metallization process control is very sensitive.

Analytical boron diffusivity model in silicon for thermal diffusion from boron silicate glass film

An analytical boron diffusivity model in silicon for thermal diffusion from a boron silicate glass (BSG) film has been proposed in terms of enhanced diffusion due to boron–silicon interstitial pair formation. The silicon interstitial generation is considered to be a result of the silicon kick-out mechanism by the diffused boron at the surface. The additional silicon interstitial generation in the bulk silicon is considered to be the dissociation of the diffused pairs. The former one causes the surface boron concentration dependent diffusion. The latter one causes the local boron concentration dependent diffusion. The calculated boron profiles based on the diffusivity model are confirmed to agree with the actual diffusion profiles measured by secondary ion mass spectroscopy (SIMS) for a wide range of the BSG boron concentration. This analytical diffusivity model is a helpful tool for p+ boron diffusion process optimization of n-type solar cell manufacturing.

Two-dimensional numerical simulation of boron diffusion for pyramidally textured silicon

Multidimensional numerical simulation of boron diffusion is of great relevance for the improvement of industrial n-type crystalline silicon wafer solar cells. However, surface passivation of boron diffused area is typically studied in one dimension on planar lifetime samples. This approach neglects the effects of the solar cell pyramidal texture on the boron doping process and resulting doping profile. In this work, we present a theoretical study using a two-dimensional surface morphology for pyramidally textured samples. The boron diffusivity and segregation coefficient between oxide and silicon in simulation are determined by reproducing measured one-dimensional boron depth profiles prepared using different boron diffusion recipes on planar samples. The established parameters are subsequently used to simulate the boron diffusion process on textured samples. The simulated junction depth is found to agree quantitatively well with electron beam induced current measurements. Finally, chemical passivation on planar and textured samples is compared in device simulation. Particularly, a two-dimensional approach is adopted for textured samples to evaluate chemical passivation. The intrinsic emitter saturation current density, which is only related to Auger and radiative recombination, is also simulated for both planar and textured samples. The differences between planar and textured samples are discussed.

Properties of boron-rich layer formed by boron diffusion in n-type silicon

A boron-rich layer (BRL) is formed during the boron diffusion process in fabricating crystalline Si solar cells. We investigated the structural, optical, and electrical characteristics of BRL in n-type silicon. A boron emitter was formed using the BBr3 liquid source in a tube furnace at 950°C. BRL had an amorphous phase. The peak concentration of boron in BRL was over 1023atoms/cm3. BRL consisted of boron, silicon, and oxygen. The oxygen atoms seemed to have caused the formation of amorphous phase. BRL showed the refractive indices of 1.5–2.0, and the contact resistance of 0.8mΩcm2.

Preparation of p+-layers using water vapour as oxidant in BBr3 diffusion for silicon solar cells

A boron diffusion process using water vapour as oxidant mixed with oxygen is introduced. Boron-doped emitter sheet resistances ranging from 30 to 400 Ω/sq and saturation current densities as low as 100 to 300 fA cm−2 for Al2O3/SiNx passivated emitters were achieved. For the predeposition process using water vapour, a low sheet resistance of 20 Ω/sq with uniformity of 5%, and a high sheet resistance of 100 Ω/sq with good in-wafer and wafer-to-wafer uniformities within 10% were achieved. With wet-oxygen predeposition method, an open-circuit voltage of 680 mV and pseudo fill factor (pFF) of 81% were obtained for the Al2O3 double-sides passivation p+/n-Si structure by the measurement of Suns-Voc. These results indicate that water vapour was suitable for forming both p+-emitters and back-surface fields for highly efficient n- and p-type solar cells.

High detection efficiency micro-structured solid-state neutron detector with extremely low leakage current fabricated with continuous p-n junction

We report the continuous p-n junction formation in honeycomb structured Si diode by in situ boron deposition and diffusion process using low pressure chemical vapor deposition for solid-state thermal neutron detection applications. Optimized diffusion temperature of 800 °C was obtained by current density-voltage characteristics for fabricated p+-n diodes. A very low leakage current density of ∼2 × 10−8 A/cm2 at −1 V was measured for enriched boron filled honeycomb structured neutron detector with a continuous p+-n junction. The neutron detection efficiency for a Maxwellian spectrum incident on the face of the detector was measured under zero bias voltage to be ∼26%. These results are very encouraging for fabrication of large area solid-state neutron detector that could be a viable alternative to 3He tube based technology.

Electro-thermal analysis of an embedded boron diffused microheater for thruster applications

One of the important design criteria of micropropulsion systems in particular VLM is the type of microheater, its layout and placement with a view to achieve uniform heating of propellant, fast heat transfer efficiency with minimum input power. Thrust produced by microthruster not only depends on the structural geometry of the thruster and propellant flow rate, but also on the chamber temperature to produce super saturated dry stream at the exit nozzle. Detailed design of microheater in thermal and electrical domains using co-solvers available in MEMS software tools along with material’s thermal property, temperature dependence of electrical resistivity and thermal conductivity have been considered in the present work to achieve precise modeling and experimental accuracy of heater operation. The chamber temperature was analytically calculated and subsequently the required resistance and power were estimated. The boron diffused microheaters of meanderline configuration in silicon substrate has been designed and its finite element based electro-thermal modeling was employed to predict the heater characteristics. The variation of microheater temperature with time, applied voltage and along chamber length has been determined from the modeling. Subsequently the designed microheater was realized on silicon wafer by lithography and boron diffusion process and its detailed testing was evaluated. It was found that boron diffused resistor of 820 Ω can generate 405 K temperature with applied input power 2.4 W. Finally the simulated results were validated by experimental data.