Point Contact Solar Cells Research Articles

Effect of back opening ratio and layout design on the performance of laser ablated point contact cell

In this paper we investigate the effect of the opening ratio and the back layout design on the electrical performance of the solar cell. First, the point contact solar cells are optimized by adjusting the laser opening ratio and the virtual-to-real ratio on each grid line of back side. The experimental results show that the open-circuit voltage (Voc) of the solar cell increases as the opening ratio decreases. Analysis of the PL images also shows that the damage to the passivation layer causes the Voc to drop. By characterizing the resistance of the back line, we found that laser drilling can cause an increase in the resistance of the back line. This can also lead to the FF loss. Then, by reducing the contact area of the bus-bar at the backside, the carrier recombination of the solar cell is reduced and the Voc of the cell is increased, resulting in a 0.07% increase in cell efficiency. Finally, the simulation shows that the openings lead to an increase in the recombination current (J01) at the base of the cell, which affects the efficiency of the cell.

Analysis of a point-contact BC-BJ silicon solar cell by three-dimensional numerical simulations

The design of optimized and efficient solar cells is a key factor for the future development of the photovoltaic (PV) technology. This paper focuses on three-dimensional (3D) modeling of a Back Contact-Back Junction (BC-BJ) crystalline silicon (c-Si) solar cells featuring a point contact (PC) scheme in the rear emitter region in order to optimize the efficiency with respect to the use of a conventional linear contact (LC) pattern. A 3D model has been built to ensure a good accuracy in the simulation of the considered solar cell structures. The developed model includes a proper modeling of the series resistance effects related to the implemented contact pattern. The TCAD Sentaurus software provided by Synopsys has been adopted to perform comparative simulations between the considered PC BC-BJ solar cell and its LC counterpart. Our simulation results prove that the adoption of a PC scheme in the emitter region of a BC-BJ solar cell is beneficial to boost its efficiency (up to 22.43%) with respect to the conventional LC cell, while keeping lower the contacted fraction of the emitter region.

Self-formed point-contact PERC solar cells

In this paper, the Al2O3 film was prepared by sol-gel method (sol-gel-Al2O3) as the rear surface passivation layer of passivated emitter rear contact (PERC) solar cells. It was found that the Al2O3 passivation layer provided a self-formed local contact, i.e. the passivation layer existed in the bottom and the inclined plane instead of the top, of the pyramid. Thus, unlike the conversional PERC solar cells, no laser ablation is used in this PERC solar cells with sol-gel-Al2O3 passivation layer. The results show that this kind of self-formed point-contact technology has very good electrical contact characteristics. This effect leads to that this PERC cellslightly surpassesthe solar cell with the full back metal contact in the fill factor (FF), which is different from the conventional PERC cell with laser ablation. It was also found thatthe introduction of sol-gel-Al2O3 passivation layer can improve the infrared lightabsorptionin the cell. By measuring the reflection of the SiN x /Si/Al2O3/Al geometry, it was directly demonstrated thatsol-gel-Al2O3 passivation layer enhanced the internal reflectionin the cell. The open circuit voltage ( V oc) and short circuit current density ( J sc) of the cell were improved, and the conversion efficiency ( η ) finally increased by 1%.

Ultrathin Cu(In,Ga)Se2 solar cells with point-like back contact in experiment and simulation

We apply the concept of point contact solar cells to a model system having 190nm thick Cu(In,Ga)Se2 (CIGSe) films by using a SiO2 back side film with periodic openings to the molybdenum layer being the electrical contact. The openings are plasma etched through a mask prepared by laser interference lithography. We find a maximum increase of the short circuit current density of 25% for a SiO2 thickness of 60nm and structure length of 1,1μm. This gain is due to (1) coherent optical reflection, (2) light scattering enhancing the quantum efficiency at all wavelengths and (3) an anticipated wave guide effect which boosts the quantum efficiency particularly at long wavelength. The best efficient solar cells with 190nm thick CIGSe has a conversion efficiency of 9% (fill factor=70%) without anti-reflection coating. These experimental results can largely be confirmed by simulation.

Characterization of Laser-Doped Localized p-n Junctions for High Efficiency Silicon Solar Cells

To further increase the efficiency of industrial crystalline silicon solar cells, a point-contact solar cell concept with localized p-n junctions is considered a promising candidate if implemented by a low cost processing technique like laser doping. For efficient development and optimization of such a processing technique, we present a dedicated test structure to derive the fundamental diode characteristics specific to the localized p-n junction, namely the contact resistance to the metal and the recombination properties, i.e., the dark saturation current. Those properties are fitted to measured dark current-voltage curves by 3-D device simulations using Quokka. We show that in particular, the contact resistance can be accurately extracted and that the method is robust against uncertainties of other device properties of the test structure. Simulations of an idealized point-contact solar cell are performed to judge the usefulness of the extractable value range with respect to the efficiency potential. Furthermore, we apply the method to laser doping experiments. We successfully characterize the recombination and contact resistance and identify a ~24% efficiency potential of a nonoptimized two-step laser doping process. Other single step processes show a very high recombination (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0pn</sub> ≫ 1e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) likely due to imperfections around the perimeter of the laser processed area.

Discrete-contact nanowire photovoltaics

A series of finite-element simulations have been performed to assess the operational characteristics of a new semiconductor nanowire solar cell design operating under high-level injection conditions. Specifically, the steady-state current-voltage behavior of a cylindrical silicon (Si) nanowire with a series of discrete, ohmic-selective contacts under intense sunlight illumination was investigated. The scope of the analysis was limited to only the factors that impact the net internal quantum yield for solar to electricity conversion. No evaluations were performed with regards to optical light trapping in the modeled structures. Several aspects in a discrete-contact nanowire device that could impact operation were explored, including the size and density of ohmic-selective contacts, the size of the nanowire, the electronic quality and conductivity of the nanowire, the surface defect density of the nanowire, and the type of ohmic selectivity employed at each contact. The analysis showed that there were ranges of values for each parameter that supported good to excellent photoresponses, with certain combinations of experimentally attainable material properties yielding internal energy conversion efficiencies at the thermodynamic limit for a single junction cell. The merits of the discrete-contact nanowire cell were contrasted with “conventional” nanowire photovoltaic cells featuring a uniform conformal contact and also with planar point-contact solar cells. The unique capacity of the discrete-contact nanowire solar cell design to operate at useful energy conversion efficiencies with low quality semiconductor nanowires (i.e., possessing short charge-carrier lifetimes) with only light doping is discussed. This work thus defines the impetus for future experimental work aimed at developing this photovoltaic architecture.

Optimization of Rear Local Contacts on High Efficiency PERC Solar Cells Structures

A local contact formation process and integration scheme have been developed for the fabrication of rear passivated point contact solar cells. Conversion efficiency of 19.6&#x25; was achieved using <svg style="vertical-align:-0.1638pt;width:66.612503px;" id="M1" height="11.225" version="1.1" viewBox="0 0 66.612503 11.225" width="66.612503" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,10.963)"><path id="x31" d="M384 0h-275v27q67 5 81.5 18.5t14.5 68.5v385q0 38 -7.5 47.5t-40.5 10.5l-48 2v24q85 15 178 52v-521q0 -55 14.5 -68.5t82.5 -18.5v-27z" /></g><g transform="matrix(.017,-0,0,-.017,8.222,10.963)"><path id="x35" d="M153 550l-26 -186q79 31 111 31q90 0 141.5 -51t51.5 -119q0 -93 -89 -166q-85 -69 -173 -71q-32 0 -61.5 11.5t-41.5 23.5q-18 17 -17 34q2 16 22 33q14 9 26 -1q61 -50 124 -50q60 0 93 43.5t33 104.5q0 69 -41.5 110t-121.5 41q-53 0 -102 -20l38 305h286l6 -8&#xA;l-26 -65h-233z" /></g><g transform="matrix(.017,-0,0,-.017,16.381,10.963)"><path id="x36" d="M137 343l67 33q37 17 63 17q79 0 129.5 -53t50.5 -131q0 -92 -58 -156.5t-147 -64.5t-147 68t-58 182q0 63 17 119t43 95.5t61.5 72t69 52t67.5 31.5q62 22 128 33l6 -32q-56 -11 -108 -35q-149 -71 -184 -231zM227 337q-47 0 -95 -27q-6 -23 -6 -70q0 -93 36 -155.5&#xA;t96 -62.5q53 0 78 45.5t25 105.5q0 68 -35 116t-99 48z" /></g><g transform="matrix(.017,-0,0,-.017,28.314,10.963)"><path id="xD7" d="M528 54l-36 -38l-198 201l-198 -201l-36 38l197 200l-197 201l36 38l198 -202l198 202l36 -38l-197 -201z" /></g><g transform="matrix(.017,-0,0,-.017,42.066,10.963)"><use xlink:href="#x31"/></g><g transform="matrix(.017,-0,0,-.017,50.226,10.963)"><use xlink:href="#x35"/></g><g transform="matrix(.017,-0,0,-.017,58.385,10.963)"><use xlink:href="#x36"/></g> </svg>&#x2009;mm, pseudo square, p-type single crystalline silicon wafers. This is a significant improvement when compared to unpassivated, full area aluminum back surface field solar cells, which exhibit only 18.9&#x25; conversion efficiency on the same wafer type. The effect of rear contact formation on cell efficiency was studied as a function of contact area and contact pitch, hence the metallization fraction. Contact shape and the thickness of Al-BSF layer were found to be heavily dependent on the laser ablation pattern and contact area. Simulated cell parameters as a function of metallization showed that there is a tradeoff between open circuit voltage and fill factor gains as the metallization fraction varies. The rear surface was passivated with an Al<sub >2</sub>O<sub >3</sub> layer and a <svg style="vertical-align:-3.27605pt;width:35.3125px;" id="M2" height="15.5125" version="1.1" viewBox="0 0 35.3125 15.5125" width="35.3125" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.363)"><path id="x53" d="M409 504l-29 -5q-16 60 -44.5 96t-86.5 36q-54 0 -82.5 -32t-28.5 -77q0 -51 30.5 -82.5t96.5 -65.5l35.5 -18t33 -19.5t33.5 -23.5l27 -25.5t24.5 -32t13.5 -36.5t6 -45q0 -80 -62 -134.5t-160 -54.5q-47 0 -98 15q-22 7 -50 21q-8 23 -27 155l30 7q7 -27 18 -52&#xA;t30 -51.5t49 -42.5t67 -16q56 0 88 32.5t32 87.5q0 51 -31.5 82t-98.5 67q-80 44 -110 73q-55 53 -55 124q0 75 56 126.5t150 51.5q53 0 126 -23z" /></g><g transform="matrix(.017,-0,0,-.017,8.018,11.363)"><path id="x69" d="M135 536q-20 0 -35 15.5t-15 35.5q0 22 15 37t36 15t35.5 -15t14.5 -37q0 -21 -15 -36t-36 -15zM252 0h-220v26q48 5 59 17t11 63v206q0 47 -9 58t-54 18v24q78 12 142 39v-345q0 -51 11.5 -63t59.5 -17v-26z" /></g><g transform="matrix(.017,-0,0,-.017,12.574,11.363)"><path id="x4E" d="M719 650v-28q-43 -2 -62 -15t-22 -44q-6 -47 -6 -169v-403h-31l-426 524h-2v-251q0 -111 6 -169q4 -37 24 -50.5t72 -16.5v-28h-237v28q45 2 64.5 16t23.5 49q6 62 6 171v220q0 54 -3 68.5t-17 32.5q-16 19 -34.5 26.5t-54.5 10.5v28h147l418 -502h3v246q0 117 -7 166&#xA;q-4 34 -24.5 47t-73.5 15v28h236z" /></g> <g transform="matrix(.012,-0,0,-.012,25.2,15.45)"><path id="x1D44B" d="M775 650l-6 -28q-60 -6 -81.5 -16t-61.5 -54l-175 -191l125 -243q30 -58 48.5 -71t82.5 -19l-5 -28h-275l7 28l35 4q31 4 37 12t-6 34l-108 216q-140 -165 -177 -219q-16 -22 -10.5 -30.5t41.5 -13.5l22 -3l-7 -28h-244l8 28q52 4 75 15.5t67 52.5q48 46 206 231&#xA;l-110 215q-26 51 -44 63t-72 17l6 28h250l-6 -28l-27 -4q-30 -5 -35 -10t3 -27q17 -43 95 -190q70 78 154 185q15 21 10 29.5t-33 12.5l-30 4l5 28h236z" /></g> </svg> capping layer. The rear surface contact pattern was created by laser ablation and the contact geometry was optimized to obtain voids free contact filling, resulting in a uniform back surface field. The efficiency gain in rear passivated cells over the reference cells is mainly due to improved short circuit current and open circuit voltage.

Performance Analysis of Rear Point Contact Solar Cells by Three-Dimensional Numerical Simulation

The adoption of local point contacts at the back surface of high-efficiency monocrystalline silicon solar cells is strategic in order to reduce the recombination losses at the rear side of the device. However, the reduction of the rear-contact surface leads to an increase of series resistance losses. In this paper, we present an extensive analysis based on 3-D optoelectronic numerical device simulations in order to highlight the dependence of the conversion efficiency on the main geometrical and technological parameters of the cell, such as the pitch and the size of the rear point contacts and the substrate resistivity. A state-of-the-art device simulator has been successfully adopted in order to accurately solve the transport equations in the semiconductor by taking into account all the loss mechanisms that are crucial in order to address the design of the cell.

후면전극형 태양전지의 고효율화를 위한 최적화 연구

This paper was carried about optimization for high efficiency of point contact solar cell. We have studied on the characteristics of power converter according to each parameter for the optimization for high efficiency of point contact solar cell on this study. We have 25.1352% of convert efficiency after adapt optimal parameters as mentioned in point body and superior conclusion is drawn by comparison with general efficiency has within 20%. At this time, the value of parameter is 100 um cell pitch, 0.01 um AR coating, 0.9 um N+ FSF thickness., etc. This study will continue to go on for optimization for efficiency in future, as it looks now, the results of this study would contribute to the business of high efficiency of point contact solar cell.

후면전극형 태양전지의 열해석에 관한 연구

This paper was carried about thermal analysis for high efficiency point contact solar cell. Therefore, we carried about 2-D device and process simulator according to design and process parameters. As a result of simulations, power transfer efficiency have decreased more increasing temperature. Especially, power transfer efficiency of room temperature have been showed 25%. The other hand, power transfer efficiency of 350 K kalvin temperature have been showed 20%. Therefore, we will considered design with thermal dissipation of device.

Interdigitated back contact solar cells with SiO2 and SiN back surface passivation

The results presented in this paper concern the study of interdigitated back contact solar cells (IBC SC) emitter passivation by means of comparison of full and point contact solar cells and two type of passivation layers (SiN and SiO2) as well as different values of the emitter sheet resistance. The fabrication of contacts in the form of points does not influence significantly the I–V characteristic parameters in comparison to full contact cells for highly doped emitters, however, improvement of Rsh is observed for a few point contact solar cells. A similar effect has been observed on higher sheet resistance emitters as well as a strong degradation of the dark current after the last annealing of the cell. We have attributed this effect to the short-circuiting of a too thin emitter.

Base limited carrier transport and performance of double junction rear point contact silicon solar cells

Abstract Rear point contact (locally diffused) solar cells with double collecting p/n junctions are investigated through numerical three-dimensional simulation and comparison with corresponding single junction solar cells. Their illuminated I–V characteristics are simulated and the series resistance of both structures is calculated. Results are presented which show the influence of the additional collecting junction to the cell's series resistance and performance. It is also shown that by biasing both junctions under slightly different voltages, the efficiency of the cell slightly increases.

Three-dimensional simulation of carrier transport effects in the base of rear point contact silicon solar cells

A method is proposed for a thorough analysis of rear point contact solar cell structures. The method is based on the numerical solution through Fast fourier transform of the minority and majority carrier transport equations in three dimensions in the base of the cell. Their illuminated current–voltage characteristics are simulated and the series resistance of the cell is calculated. Results are presented which show the influence of the rear contact size and the majority transport in the base to the solar cell performance.

A study of shading and resistive loss from the fingers of encapsulated solar cells

Optimised solar cell design is dependent on the assumed shading and resistance losses associated with front contacts. In this study, a spectrophotometer with integrating sphere attachment was used to measure the reflection from the front surface of encapsulated silver electroplated front contact solar cells. The results obtained are in good agreement with a previous study by one of the authors using a different method. The measured effective shading loss is about one third of the coverage fraction of the cell grid because of trapping of light reflected from the grid. The grid loss in 4×5 cm silver electroplated front contact solar cells was found to be similar to the predicted loss from buried grid and rear point contact solar cells operating at 30 suns concentration.

On the origin of photocurrent oscillation at Si electrodes

Photocurrent oscillations at n-type Si(100) were investigated in ammonium fluoride solutions for a variety of electrolyte compositions and pH values. The data show a linear correlation between the etch rate for anodic oxides and the oscillation frequency at fixed applied voltage. A model based on minority carrier collection at the boundary between pores and the silicon substrate is suggested. Because of the large diffusion length of holes in silicon, the strong photocurrent modulation observed can be explained by changes in a relatively small number of charge-collecting pores while a substantial overall oxide thickness is maintained. A transition to noisy behaviour is also observed when the solution composition is changed to give a higher etch rate. The charge collection model used here to interpret the photocurrent oscillation is also the basic functioning principle of silicon point contact solar cells.

Use of ultrathin oxides and thin polycrystalline silicon films for stable high-efficiency silicon solar cells

Initial designs of single-crystal point-contact solar cells showed a degradation in their efficiency due to photoinjected hot-electron damage. We have examined the ultraviolet stability of ultrathin oxides covered by a thin polycrystalline silicon film and a thick oxide. Optical modeling has shown that these oxide/polycrystalline silicon/oxide stacks can have extremely good antireflection properties which offset the absorption losses from the polycrystalline silicon. Experiments have determined that these stacks are stable under ultraviolet exposure and that the polycrystalline silicon is absorbing less light than predicted. Point-contact solar cells fabricated with this technique have achieved efficiencies as high as 24.4% under 36 W/cm2 of concentrated sunlight.

Photoinjected hot-electron damage in silicon point-contact solar cells

Initial designs of single-crystal silicon point-contact solar cells have shown a degradation in their efficiency after being exposed to concentrated sunlight. The main mechanism appears to be an increase in recombination centers at the Si/SiO2 interface due to ultraviolet light photoinjecting electrons from the silicon conduction band into the silicon dioxide that passivates the cell’s front surface. The instability of the interface is significantly worse if the oxide is grown in the presence of trichloroethane. Texturization of the surface also leads to more instability. A reasonably good resistance to ultraviolet can be created by putting a phosphorus diffusion at the surface, and can be improved further by stripping off the deposited oxide after the diffusion and regrowing a dry thermal oxide.

Doped surfaces in one sun, point-contact solar cells

This letter reports two new types of large-area (&amp;gt;8.5 cm2), backside, point-contact solar cells with doped surfaces, designed for use in unconcentrated sunlight. One type was fabricated on an intrinsic substrate with an optimized phosphorus diffusion on the sunward surface. The apertured-area efficiency was independently measured to be 22.3% at 1 sun (0.100 W/cm2), 25 °C, the highest reported for a silicon solar cell. The other type is constructed on a doped substrate, and has an apertured-area efficiency of 20.9%, the highest reported for a point-contact solar cell with a base in low-level injection. Both cells have record open-circuit voltages above 700 mV.

Light-induced degradation at the silicon/silicon dioxide interface

Single-crystal silicon point-contact solar cells show a degradation in their efficiency after being exposed to concentrated sunlight. This change has been linked to an increase in the surface recombination velocity. A similar effect is produced by carrier injection under forward bias. The annealing kinetics, the role of ultraviolet light, and possible causes for the creation of surface states are discussed.

Design criteria for Si point-contact concentrator solar cells

Design criteria for concentrator solar cells are presented for the highly three-dimensional case of backside point-contact solar cells. A recent new experimental result, a 28-percent efficient cell (25°C, 15-W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> incident power) is used as a case study of the dependences of the recombination components and the carrier density gradients on the geometrical design parameters. The optimum geometry is found to depend upon the intended design power density as well as the attainable physical parameters allowed by the fabrication techniques utilized. Modeling projections indicate that an ultimate efficiency of 30.6 percent (36 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 300 K) is achievable using the diffused emitters presently employed on these cells. Incorporation of results from the study of polycrystalline emitters could improve these efficiencies toward 31.7 percent.