High-efficiency interdigitated back-contacted Si heterojunction (IBC-SHJ) cells for tandem applications

Leuven - PhD
More than two weeks ago

Opening the avenue towards 30%+ solar cells by developing a specifically optimized Si bottomcell


Photovoltaics (PV) is the fastest growing electrical energy generation source in the world. The cumulative installed capacity of PV has already surpassed 500 GW in 2018 and within the next decade, annual PV production is expected to reach 1 TW/year, ushering in the global energy transition. In such exciting times, the main economic driving force in the PV industry is still the reduction of PV module cost per Watt peak. As the crystalline Si (c-Si) module costs continue to drop, the balance-of-system (BOS) costs become important. Since the BOS costs scale with installation area, higher efficiency modules which produce more power per unit area are preferred. Therefore, developing high-efficiency cell concepts for the future is of great interest in the R&D world.

The PV industry has been transitioning from Al-BSF solar cells to PERC solar cells in order to increase the module efficiencies. The focus of next-generation solar cell technology development has now turned towards reducing contact recombination. For this, solar cells with passivated contacts are being widely investigated, such as (1) tunnel oxide + poly-Si contacts, (2) low-temperature all-Si heterojunction contacts, and (3) transition metal oxide-based carrier-selective contacts. At imec, all three routes are being investigated. Si heterojunction (HJ) cells with an interdigitated back-contact (IBC) architecture are the most efficient Si solar cells in the world today, with Kaneka breaking the world record efficiency with its remarkable 26.7% cell [1], getting quite close to the theoretical and practical limit for single-junction Si solar cells.

To go beyond the fundamental single-junction limit, a tandem device architecture, which employs 2 or more absorber materials of complementary bandgaps in a stack, must be adopted to reduce thermalisation losses and use the solar spectrum more effectively. A wide bandgap perovskite top cell above a c-Si bottom cell is one of the emerging tandem solar cell configurations that has attracted plenty of recent interest, due to its potential of exceeding 30% while combining the attractive properties of perovskites with the well-understood technologies for c-Si. The best monolithic implementation of this material combination was achieved by Oxford PV with an efficiency of 27.3%.

This PhD thesis proposal focuses on the implementation and advancement of the IBC-SHJ cell technology for use as a bottom cell in a perovskite/IBC-SHJ tandem. The first part of this work will focus on the investigation of the loss mechanisms in the IBC-SHJ cell technology of imec, in particular, the interplay between charge-carrier transport and passivation properties of the thin-film contact layers. New materials, architectures and processes will also be investigated. Based on the understanding gained, improvements to the device performance will be made step-by-step, targeting an efficiency of ~26% for a standalone device. In the second part, the developed high-efficiency IBC-SHJ cell technology will be tailored for use as a bottom cell in a perovskite/IBC-SHJ tandem, considering the filtered solar spectrum received by the bottom cell, which depends on the film properties of the top cell. Thus, co-design of the entire tandem must be taken into consideration for achieving optimal opto-electrical performance. Advanced light management structures based on nano-texturing will be investigated for improving near-IR light trapping. Upscaling and development of a lean process flow will be an integral part of this thesis. This work will be performed in close collaboration with the thin-film group, which is developing the perovskite top cell. The thesis will culminate in the integration of a perovskite top cell on a tailored IBC-SHJ c-Si bottom cell, achieving efficiencies >29%. Module integration of tandem devices will also be initiated during this PhD work.

[1]         K. Yamamoto, K. Yoshikawa, H. Uzu, and D. Adachi, "High-efficiency heterojunction crystalline Si solar cells," Jpn. J. Appl. Phys., vol. 57, pp. 08RB20-1, 2018.​​

Required background:  

  • Master of Science or Master of Engineering
  • Curious, autonomous and dynamic
  • Team player
  • Strong feeling for/experience in practical work

Type of work: 15% literature study + 15% modeling + 70% experimental

Supervisor: Jef Poortmans

Daily advisor: Filip Duerinckx, Hariharsudan Sivaramakrishnan Radhakrishnan

The reference code for this position is 2020-065. Mention this reference code on your application form.
Chinese nationals who wish to apply for the CSC scholarship, should use the following code when applying for this topic: CSC2020-27.


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