Selective Emitter Technology Research Articles

22.56% total area efficiency of n-TOPCon solar cell with screen-printed Al paste

Screen-printing Ag paste on the rear side of the Tunnel Oxide Passivated Contact solar cells (TOPCon) is still the mainstream method to form electrodes. However, the high price of precious metals increases the cost of TOPCon cells. Al is a cheap and high-performance conductor, and its work function is compatible with the rear side of TOPCon cells. In this study, we used a UV pulse laser (355 nm, 10 ps) to ablate the rear side SiNx passivation layer of TOPCon cells and then printed Al paste with different weight percentages of silicon (Si-wt.%) on the phosphorus-doped polycrystalline silicon (n+-poly-Si) layer to reduce the cost. We investigated the damage mechanism of laser on SiOx/n+-poly-Si/SiNx passivation structure and the contact mechanism between Al paste and n+-poly-Si layer. The results show that the Voc of SiOx/n+-poly-Si/SiNx passivation structure reduced about 6–7 mV when the laser energy density was 0.431 J/cm2. We got the best electrical performance of TOPCon cells printed with Al paste (25 wt%-29 wt% silicon). The open-circuit voltage (Voc) and the conversion efficiency (Eff), have reached 663.60 mV and 22.56 % respectively. Although the efficiency was 9.40 % relative lower than that of TOPCon cells printed with Ag paste, but the cost of Al paste only accounted for 10 % of Ag paste. In the future, the highest Eff of TOPCon solar cells printed with Al paste on the rear side are expected to reach the commercial TOPCon based on Ag paste, which applies laser doping selective emitter technology (SE) and bifacial poly-Si passivation structure.

N-TOPCon 태양전지의 선택적 에미터 형성 기술 분석

The main efficiency limiting factors for homogeneous emitter solar cells are resistance loss through metal contact on the front side and recombination loss at the surface. Herein, a selective emitter technology is introduced to solve the above problem, and it is currently commercialized in the mainstream p-PERC (Passivated Emitter Rear Contact) solar cell. The selective emitter boosts efficiency by 0.3~0.4% when compared to a homogeneous emitter, and when applied to the n-TOPCon (Tunnel Oxide Passivated Contact) solar cell, high efficiency of 26% or higher may be predicted. The most widely utilized selective emitter technologies are laser and etch-back. The One-Step Technology, which is suited to the n-TOPCon solar cell process, a laser is suitable for mass manufacturing with high yield. Because selective emitters increase electrical characteristics, which impact cell efficiency, it is required to study and create a technology that is optimal for the n-TOPCon manufacturing process.

Selective emitter technology global implantation through the use of low ultraviolet cut-off EVA

Selective emitter diffusion technology has demonstrated a direct PV cell efficiency increase, due to a good ohmic contact and high blue response. These PV devices will be assembled to fabricate the final and commercial PV modules where the power enhancement is the most valuable one. The traditional encapsulant material is ethylene-vinyl-acetate (EVA) which ultraviolet wavelength cut off is placed in the region where selective emitter technology improvement is performed. Photovoltaic industry has developed innovate materials to overcome these issues. Among them, a low ultraviolet cut off EVA can be easily acquired. Our study demonstrates that with the correct PV module encapsulant configuration, part of the developed PV cell efficiency improvement related to selective emitter technology can be successfully translated at the end of the value chain; that is, the final PV module.

Industrial 6 Inch Multicrystalline Silicon Solar Cells Fabricated Using Reactive Ion Etching with Efficiency Exceeding 18%

To obtain a lower reflectance, we applied a maskless plasma texturing technique by reactive ion etching (RIE) to acid-textured multicrystalline silicon (mc-Si) wafer. RIE texturing produced a deep and narrow textured surface with an excellent low reflectance. Owing to plasma-induced damage, unless the RIE-textured surface is subjected to proper damage removal etching (DRE), it shows drops in open circuit voltage (Voc) and fill factor (FF). RIE-textured samples with proper DRE showed sufficiently higher short circuit current (Isc) than acid-textured samples without a drop in Voc. In this study, we applied RIE texturing under optimized DRE condition to the selective emitter structure. In comparison with the acid-textured solar cells, RIE-textured solar cells have absolute gains in Isc above 200 mA. We successfully fabricated a 6-in. mc-Si solar cell with a conversion efficiency exceeding 18% by applying selective emitter technology with RIE texturing.

18.3% Efficiency on High Ohmic Emitters without Selective Emitters

Crystalline silicon solar cells with high ohmic emitters show higher efficiencies due to a better blue response. Unfortunately, the only way to contact them by screen printing is using the selective emitter technology. This study shows that contacting emitters with Rsh = 100Ω/sq can be achieved by standard screen printing technology without selective emitter processing thanks to the development of a new silver paste. Thus, no additional process steps are needed to selectively dope the emitter. We study the electrical properties of industrially processed c-Si solar cells, with two different screen printing silver pastes (Pastes A and B) and emitters with sheet resistances Rsh = 80Ω/sq, 100Ω/sq, and laser doped selective emitter with Rsh = 20Ω/sq on Rsh = 100Ω/sq. On the solar cells with 80Ω/sq emitter, paste B yields a low series resistance Rs = 0.72Ω cm2, thanks to its lower contact resistance ρc and its lower penetration into the space charge region, compared to paste A. The low series resistance leads to an efficiency gain Δη = 0.7%abs. We also obtain promising results on 100Ω/sq, as the contact resistance ρc ≤ 3.1 mΩcm2 leads to a maximum fill factor FF = 78.8%. The efficiency η = 18.3% of the 100Ω/sq emitter solar cells is then comparable to the one of the selective emitter cells. With paste B, we demonstrate that it is now possible to contact high ohmic emitters, without the use of a selective emitter structure.

Improving the efficiency of crystalline silicon solar cells by an intersected selective laser doping

The selective emitter technology is the most effective method to improve the silicon solar cell performance. However, the strict alignment requirements between the Ag gridlines and the selective emitters should be addressed. In the present study, a novel front metal contact patterning scheme for crystalline silicon (c-Si) solar cells is developed. An intersected selective laser doping process is applied. The control experiment indicates that the best efficiency increases for ∼23.8% from ∼14.39% to ∼17.74% after receiving the laser doping process. Moreover, our laser doping process does not affect the open-circuit voltage and short-circuit current significantly and the emitter properties have not been degraded in terms of the emitter saturation current. The improved front metal contact results in the improved energy conversion efficiency. The developed process offers an elegant and reliable approach for the low-cost, high throughput industrial-scale production process.

Implementation of Highly Resistive Emitter Solar Cells in a Production Environment using an Inline Doping System

Instead of selective emitter technology we investigate an alternative way to optimize contact formation and increased blue responsivity of highly resistive emitter solar cells using screen print technology for the deposition of the frontside metallization grid. We show with the aid of an inline doping/diffusion set-up at Blue Chip Energy that tuning the emitter doping profile is an alternative way to reduce the effect of Auger recombination in the spectral range from 300 nm to 600 nm. By properly choosing the process conditions we were able to minimize the detrimental effect of the low surface concentration of the dopant on the contact resistance. Due to improved blue light responsivity a significant gain in short circuit current Jsc was achieved. This and a reduced reverse saturation current I00E yielded a higher open circuit voltage VOC and an increase of cell efficiency from 17.6 %-avg to more than 17.9 %-avg.

Record Large-Area p-Type CZ Production Cell Efficiency of 19.3% Based on LDSE Technology

A record independently confirmed production cell efficiency of 19.3% is presented for a large-area p-type Czochralski (CZ) silicon solar cell, based on the University of New South Wales (UNSW) laser-doped selective emitter technology. In this paper, the innovative and patented laser-doping technology is simply added to a standard Centrotherm turnkey line, operating with a modified process and the addition of the laser-doping and light-induced plating steps. Impressively, this record efficiency is achieved by using standard commercial grade p-type CZ-grown silicon wafers on standard production equipment and exceeds the previous independently confirmed record for any technology of 19.2% using a standard aluminum back-surface field with full rear coverage. The avoidance of laser-induced defects is discussed in this paper to overcome previous limitations of the laser-doping technology using conventional Q-switched lasers or the laser chemical processing method. It is demonstrated that the use of appropriate lasers can avoid defect formation through thermal cycling while still allowing for the sufficient mixing of dopants and allow laser doping to be performed through a standard SiN layer with contacts formed through a self-aligning metallization scheme.