LED solar simulators and new test approaches for high-efficiency solar cells

By Marko Turek; Kai Sporleder; Christian Hagendorf

Solar simulators are among the most important and fundamental measurement tools in photovoltaic production facilities as well as in R&D labs. Two major solar simulator technologies can be distinguished: xenon light sources and, more recently, light sources using light-emitting diodes (LEDs). While xenon solar simulators are a well-established technology, LED-based systems appear to be promising candidates for future applications, as they provide a higher flexibility with regard to the flash times, spectral light composition and intensity. Measurement recipes for power quantification under standard test conditions (STC) can be adapted to high-efficiency cells, which require longer flash times. Furthermore, fast inline spectral testing, such as a rapid external quantum efficiency (EQE) test or a rapid reflectivity test, becomes feasible. However, the development of LED-based systems requires well-designed optical and electronic components to ensure high-precision measurements on the basis of a laterally uniform and temporally stable light field.

Beyond boron–oxygen deactivation: Industrially feasible LID-free p-type Czochralski silicon

By Bianca Lim; Agnes Merkle; Robby Peibst; Thorsten Dullweber; Yichun Wang; Rui Zhou

Today’s industry-standard B-doped monocrystalline silicon still suffers from light-induced degradation (LID) of the carrier lifetime. Illumination at elevated temperatures leads to a so-called regeneration, i.e. a recovery of both the carrier lifetime and the solar cell efficiency. However, even though the carrier lifetime on test wafers increases from about 1ms after processing to 3ms after regeneration, the corresponding PERC+ cell efficiencies in both states are identical; possible reasons for this discrepancy are discussed in this paper.

Solving all bottlenecks for silicon heterojunction technology

By Christophe Ballif; Mathieu Boccard; Antoine Descoeudres; Christophe Allebé; Antonin Faes; Olivier Dupré; Jan Haschke; Pierre-Jean Ribeyron; Matthieu Despeisse

Silicon heterojunction (SHJ) solar cells are the archetypes of ‘fullsurface passivating contact’ solar cells; such contacts are required in order to achieve typical open-circuit voltages of up to 730–750mV. Although SHJ technology has fewer manufacturing steps and enables higher efficiencies than standard passivated emitter and rear cell (PERC) technology, the market has been slow in taking it up. This paper discusses some of the obstacles that have been overcome in the last 10 years, and shows why the technology is now readier than ever for a competitive mass-market launch.

Low-cost standard nPERT solar cells towards 23% efficiency and 700mV voltage using Al paste technology

By Radovan Kopecek; Zih-Wei Peng; Thomas Buck; Corrado Comparotto; Valentin D. Mihailetchi; Lejo J. Koduvelikulathu; Joris Libal; Jan Lossen; Masahiro Nakahara; Kosuke Tsuji; Marwan Dhamrin; Wolfgang Jooss

Stable high voltages in solar cells and modules are becoming increasingly important as large PV systems are being set up in desert regions and are therefore exposed to high temperatures. High-voltage solar cells have lower temperature coefficients and thus produce a higher energy yield for such PV systems. Standard passivated emitter rear cell (PERC) devices have moderate voltages below 680mV, and also have the risk of degrading in such regions, because of light and elevated-temperature induced degradation (LeTID) effects and, in more recent observations, passivation degradation. This paper presents a solution for PERC producers to easily make the switch to n-type passivated emitter, rear totally diffused (nPERT) solar cells, which are capable of stable efficiencies above 22% and voltages close to 700mV, at almost no additional cost.

Pioneering the industrialization of PERC technology: A review of the development of mono- and bifacial PERC solar cells at SolarWorld

By Phedon Palinginis; Christian Kusterer; Stefan Steckemetz; René Köhler; René Härtwig; Torsten Weber; Matthias Müller; Gerd Fischer; Holger Neuhaus

SolarWorld has played a pioneering role in triggering and implementing the shift from p-type multicrystalline aluminium backsurface field (Al-BSF) to p-type monocrystalline passivated emitter and rear cell (PERC) as the next mainstream solar cell technology, and recognized PERC to be the door opener to an extremely simple and cost-effective implementation of a bifacial solar cell. This paper reviews PERC technology development at SolarWorld, featuring an industrial baseline process for monocrystalline five-busbar (5BB) p-type PERC solar cells exceeding 22.0% median (22.5% maximum) cell efficiency by May 2018, before operations at SolarWorld came to a final halt.

Metallization and interconnection for high-efficiency bifacial silicon heterojunction solar cells and modules

By Antonin Faes; Agata Lachowicz; Armand Bettinelli; Pierre-Jean Ribeyron; Jonas Geissbühler

Silicon heterojunction (SHJ) solar cells demonstrate a high conversion efficiency, reaching up to 25.1% using a simple and lean process flow for both-sides-contacted devices, and achieving a record silicon solar cell efficiency of 26.7% in back-contacted configuration. In addition, the field advantages of SHJ cell technology are a native bifaciality and low thermal coefficient providing impressive energy yield. Finally, the technology demonstrates potential cost reduction as it is perfectly suited for thin wafers integration. The SHJ technology is therefore today triggering strong interest in the PV industry, appearing on the roadmap of different cell manufacturers, with several production lines and pilot lines being installed worldwide. One limiting factor of the technology is related to the metallization: due to temperature restrictions on heterocontacts, the standard firing through silver paste needs to be replaced by low curing temperature paste. This type of pastes yield fingers with higher bulk resistivity (two to three times the one obtained with high temperature cured silver pastes) and lower adhesion after soldering. In this paper, materials, processes and costs figures will be reviewed for the metallization and module integration of SHJ solar cells, with a focus on copper plating benchmarked to silver screen-printing, for varying module interconnection technologies.

Riding the workhorse of the industry: PERC

By Pietro P. Altermatt; Yifeng Chen; Yang Yang; Zhiqiang Feng

Improving PERC cells requires rather different strategies than standard cells have required, demanding concrete improvements in materials, manufacturing procedures and fabrication tools.

On the fabrication of high-efficiency mc-Si PERC-based solar cells on diamond wire-sawn surfaces using industrially viable etching technologies

By Bishal Kafle; Pierre Saint-Cast; Ahmed Ismail Ridoy; Sebastian Nold; Jonas Schön; Marc Hofmann; Jochen Rentsch; Laurent Clochard; Edward Duffy

Improving the texturing approach for diamond wire-sawn (DWS) multicrystalline silicon (mc-Si) wafers is one of the key steps to decrease its efficiency gap with monocrystalline silicon-based solar cells. In this regard, black silicon texturing has increasingly caught attention of both academia and industries as a potential approach towards mass production of high-efficiency mc-Si solar cells. In this paper, the challenges of implementing such a texture, with unique feature sizes, in mass production are discussed in detail, and the latest results are reviewed. Finally, results of the first trials at high volume manufacturer applying an alternative plasma-less dry-chemical etching (ADE) method are presented.

Solutions to realizing LID-controlled multi-PERC cells and modules

By Fangdan Jiang; Jan-Nicolas Jaubert; Daqi Zhang; Zheng Yao; Guangyong Xiong; Jian Wu; Guoqiang Xing, Canadian Solar Inc., Suzhou, Jiangsu, China

State-of-the-art black-silicon texturing technology has been successfully implemented in all of the 4.5GW multi-Si cell production lines at Canadian Solar (CSI). With a combination of black-silicon texturing and diamondwire-sawn wafers, it has been possible to increase cell efficiency and wattage, while significantly reducing the cost. To further improve CSI’s multi-Si product performance and cost, multi-Si passivated emitter rear contact (multi-PERC) technology has been developed to achieve a mass production cell efficiency of more than 20% on average, and a module power exceeding 300W. By the end of 2017, a production capacity of over 1GW had been established, and CSI’s majority multi-Si cell capacity will be upgraded to PERC in 2018. This paper will introduce the solutions to realizing light-induced degradation (LID)-controlled multi-PERC cells and modules, as well as offering a discussion of the degradation performance. In addition, the technology evolution of CSI’s high-efficiency multi-Si products and a roadmap for 22%-efficiency multi-Si cells are presented.

Towards industrial manufacturing of TOPCon

By Frank Feldmann; Sebastian Mack; Bernd Steinhauser; Leonard Tutsch; Jana-Isabelle Polzin; Jan Temmler; Anamaria Moldovan; Andreas Wolf; Jochen Rentsch; Martin Hermle; Stefan W. Glunz, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany

TOPCon is regarded as a possible follow-up technology to the passivated emitter and rear cell (PERC) concept. This paper presents the latest results for high-efficiency solar cells, and the progress made on migrating layer deposition to high-throughput tools, which are already in use in industry. Possible metallization approaches, and three different industrially relevant solar cell structures featuring TOPCon, are also discussed.

ECN’s IBC solar cells in mass production environment: rise of a competitive back-contact module concept

By Antonius R. Burgers; Ilkay Cesar; Nicolas Guillevin; Arthur W. Weeber; Jan M. Kroon, ECN Solar Energy, Petten, The Netherlands

We present an n-type bifacial IBC solar cell that uses a simple process comparable to our industrially proven n-type cell process for conventional H-grid front- and rear-contacted n-PERT cells. The process is based on tube diffusion and a simultaneous single-step screen-print of the contacts to both polarities, and has been demonstrated on an industrial line at pilot scale.

Bifacial solar products light new pathway to future PV

By Peiting Zheng; Xinyu Zhang; Junhui Liu; Xueting Yuan; Li Zha; William Chen; Hao Jin, JinkoSolar

Relatively few experimental and academic studies about bifacial p-type PERC cells have been published to date. This paper looks at the experimental findings from JinkoSolar’s large area, industry-grade bifacial monocrystalline silicon PERC (biPERC) cells.

‘Less is more’: Ultrathin heterojunction cells offering industrial cost reduction and innovative module applications

By Eric Gerritsen; Samuel Harrison; Julien Gaume; Adrien Danel; Jordi Veirman; Felix Gerenton; Thomas Guerin; Maryline Joanny; Charles Roux & Yannick Veschetti

Because of its symmetrical a-Si/c-Si/a-Si structure, silicon heterojunction (SHJ) cell technology offers the possibility to use much thinner wafers, and thus to reduce material and production cost. In order to evaluate the industrial feasibility of these thinner heterojunction cells, wafers from the standard thickness of 160μm down to 40μm were processed on the heterojunction pilot line at CEA-INES.

Texture etching technologies for diamond-wire-sawn mc-Si solar cells

By Jochen Rentsch, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany; Bishal Kafle; Marc Hofmann; Katrin Krieg; Martin Zimmer

Optical confinement is essential in order to increase the amount of photogeneration in a crystalline silicon (c-Si) solar cell. Fraunhofer examines the compatible options for wafers created using diamond wire sawing.

Industrialized high-efficiency mono PERC cells

By Dr. Zhang Guanlun, TongWei Solar (Chengdu) Co. Ltd., P. R. China; Lan Wang; Junmin Wu; Qing Chang; Tao Yan; Yaohui Xie; Lei Yang; Bushuang Hong; Yuanqiu Zhang; Peng Zhang; Bingwei Yin

The deployment of renewable energy, especially solar, is becoming ever more popular. It is estimated that with every 1% increase in PV cell efficiency, electricity costs would decrease by 7%; therefore, improving solar cell efficiency is very important for reducing the average electricity-generating cost of solar and driving it towards grid parity.