Elsevier

Renewable Energy

Volume 146, February 2020, Pages 1676-1681
Renewable Energy

Optimization of PERC fabrication based on loss analysis in an industrially relevant environment: First results from GÜNAM photovoltaic line (GPVL)

https://doi.org/10.1016/j.renene.2019.07.149Get rights and content

Highlights

  • Pilot lines bridge lab scale proven concepts with the products which are ready for mass production.

  • PERC technology has gained up to 21% market share along all Si based technologies.

  • Detailed loss analysis helps to draw roadmaps for higher efficiencies.

  • 19.21% efficiency PERC was fabricated in pilot environment as expected by loss analysis.

Abstract

Passivated emitter and rear cell (PERC) concept with an already developed roadmap for 24% efficiency will be leading the photovoltaics industry in the upcoming years. In a few industrial pilot lines, efficiencies above 22% have already been attained. Pilot lines have important roles in bridging lab scale proven concepts with the products which are ready for mass production. Therefore, GUNAM Photovoltaic Line which is specialized on PERC concepts has been established to overcome the barriers that hinder the performance of c-Si solar cells in PERC concepts in a relevant environment. The aim of this article is to show how a loss analysis can be employed in a practical way in an industrially relevant environment. The analysis depends on the first results of the studies from 6 months ramp up period of GPVL. A batch of standard PERC type solar cells with p-type base and atomic layer deposited Al2O3 rear passivation have been fabricated during the ramp up of the line. A detailed gain-loss analysis was performed to address the optical, electrical and recombination losses in order to increase the cell efficiency.

Introduction

PERC technology has gained up to 21% market share along all Si based technologies and projections foresee that this share will reach up to 60% until 2028 [1]. The success of PERC stems from its rear side structure. The high open circuit voltage (VOC) is a result of excellent rear side passivation. Secondly, the high short circuit current (ISC) potential is due to enhanced rear side reflection and decreased parasitic absorption [2]. On the other hand, since the line utilized for PERC fabrication requires only a slight differentiation from conventional ones with industrially available tools, this technology takes its place in the c-Si solar cell market as an advantageous option. With these lines, industrial efficiencies as high as 22.6% have been attained for PERC of which roadmap for 24% efficiency has already been developed [3,4]. It is close to the record c-Si efficiency 26.7% of today that uses advanced/expensive production techniques [5].

Pilot lines play an important role on transferring the knowledge from laboratory to industrial scale. Equipped with medium to high throughput tools and holding advantage of flexibility in both process conditions and sequence make pilot lines perfectly suitable environments for industrial process development. Center for Solar Energy Research and Applications (GÜNAM) established Turkey's first pilot production facility GÜNAM Photovoltaic Line (GPVL) in 2017 with the aim of development of PERC type c-Si solar cells. The line is fully equipped with the tools to fabricate PERC structure at a gross throughput of 100 wafers/hour while some individual tools can go up to 1400 wafers/hour capacity.

This paper is based on the results of the first two generations of PERC fabrication in GPVL. Followed by optimization of each tool for the specific process, cells were fabricated in the pilot line to observe the baseline efficiency at first hand. Then the loss analysis was employed to show how the first optimization can be easily achieved with significant gains. All necessary characterizations were carried out to address the losses for which the synergetic effects were taken into account via the synergetic efficiency gain analysis (SEGA) method as described in Ref. [6]. After solving the issues related to one of the dominant losses that specified, the second generation cells with the highest efficiency of 19.21% were obtained together with the possible routes for enhancement of the efficiency to higher values in the coming generations.

Section snippets

Experimental

In order to fabricate PERC type solar cells, a process flow as depicted in Fig. 1 was designed. The required parameters for synergistic efficiency gain analysis (SEGA) [7], were extracted from the characterization results performed at relevant step and common values beyond the measurement techniques of our lab were acquired from the literature as shown in Table 1. For this purpose, three process flows as shown in Fig. 1 have been followed during manufacturing of solar cells, namely “emitter

Front & rear doping

Fig. 2 depicts the active dopant profiles for the front industrial emitter and local rear aluminum back surface field. The junction depth for the phosphorus emitter is at 600 nm from the surface and sheet resistance is calculated to be 71 Ω/□. Similarly, local BSF depth is 6  μm and sheet resistance of the Al doped layer is Ω/□.

Front emitter and bulk lifetime characterization via symmetrical lifetime samples after passivation and firing are shown in Fig. 3. From Fig. 3a, which shows the

Conclusion

PERC technology is the most promising technology for the industrial PV applications due to process simplicity and efficiency potential. In this study, the first results of the newly founded photovoltaic pilot production facility “GPVL” were reported. Methodology used for development of the efficiency of the cells was making a detailed loss analysis which takes into account the synergetic effects resulting from different mechanisms and solving the biggest problems in the following run. With this

Funding

This study was substantially carried out in the scope of 113G113 MİLGES Project funded by The Scientific and Technological Research Council of Turkey (TÜBİTAK).

References (12)

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1

Gülsen Baytemir is now with Maltepe University, Faculty of Engineering and Natural Sciences, Maltepe & İstanbul. E-mail: [email protected].

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