The high usage of silver in industrial solar cells may limit the growth of the solar industry. One solution is to replace Ag with copper. A screen printable Cu paste is used herein to metallize industrial interdigitated back contact (IBC) solar cells. A novel metallization structure is proposed for making solar cells. Cu paste is applied to replace the majority of the Ag used in IBC cells as busbars and fingers. Cu paste is evaluated for use as fingers, and solar cells are made to test conversion efficiency and reliability. The Cu paste achieves comparably low resistivity, and Cu paste printed cells demonstrate similar efficiency to Ag paste printed cells, with an average efficiency of 23%, and only 4.5 mg W−1 of Ag usage. Also, the solar cells are stable and no Cu in-diffusion is observed under damp heat (85 °C, 85% relative humidity) and thermal stress (200 °C) for 1000 h, respectively. All processes used in this study can be carried out with industrial equipment. These findings reveal a new application for Cu pastes and point to a new direction for reducing Ag utilization and cost.@en

The EU crystalline silicon (c-Si) PV manufacturing industry has faced strong foreign competition in the last decade. To strive in this competitive environment and differentiate itself from the competition, the EU c-Si PV manufacturing industry needs to (1) focus on highly performing c-Si PV technologies, (2) include sustainability by design, and (3) develop differentiated PV module designs for a broad range of PV applications to tap into rapidly growing existing and new markets. This is precisely the aim of the 3.5 years long H2020 funded HighLite project, which started in October 2019 under the work program LC-SC3-RES-15-2019: Increase the competitiveness of the EU PV manufacturing industry. To achieve this goal, the HighLite project focuses on bringing two advanced PV module designs and the related manufacturing solutions to higher technology readiness levels (TRL). The first module design aims to combine the benefits of n-type silicon heterojunction (SHJ) cells (high efficiency and bifaciality potential, improved sustainability, rapidly growing supply chain in the EU) with the ones of shingle assembly (higher packing density, improved modularity, and excellent aesthetics). The second module design is based on the assembly of low-cost industrial interdigitated back-contact (IBC) cells cut in half or smaller, which is interesting to improve module efficiencies and increase modularity (key for application in buildings, vehicles, etc.). This contribution provides an overview of the key results achieved so far by the HighLite project partners and discusses their relevance to help raise the EU PV industries' competitiveness. We report on promising high-efficiency industrial cell results (24.1% SHJ cell with a shingle layout and 23.9% IBC cell with passivated contacts), novel approaches for high-throughput laser cutting and edge re-passivation, module designs for BAPV, BIPV, and VIPV applications passing extended testing, and first 1-year outdoor monitoring results compared with benchmark products.@en

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.@en

The edge recombination losses of crystalline silicon solar cells become significant when they are cut into smaller pieces to be assembled into modules. With the interdigitated pattern of doped p and n regions on the rear side, the interdigitated back contact (IBC) solar cells can be cut through different doped regions. In this study, the cutting losses in IBC solar cells are investigated and various cutting scenarios are studied. Through simulations and experimental measurements, it is found that the cut losses can be reduced by cutting through the back surface field rather than through the emitter. The losses under low light intensity are reduced to an even greater extent. When a 23% cell is cut into 1/3 pieces, the efficiency can be increased by 1.2%rel (cut related losses were improved from 2.0rel to 0.8%rel under standard 1-sun testing conditions, compared to cutting through the emitter. Under low light intensity of 0.25 sun, the improvement is around 2.4%rel. The improvement is mainly due to lower FF losses in the I-V characteristics, and this is further confirmed by Suns-Voc and PL measurements. In the pFF analysis, the additional losses due to laser damage are also observed. This strategy of cutting through the BSF region in IBC solar cells can be quickly adopted in mass production without the need for additional processes or equipment and both module power and energy yield can be increased.@en

The issue of climate change, including global warming, poses a significant challenge to our planet. In response to this challenge, the Paris Agreement was signed, which aims to limit the rise in global temperatures to well below 2 ◦C and pursue efforts to limit it even further to 1.5 ◦C. Photovoltaic energy is the key to achieving this target. This dissertation focuses on improving the efficiency and sustainability of interdigitated back contact (IBC) solar cells. A special emphasis is also placed on cost and reliability. IBC cells and modules utilized in this study are based on ZEBRA technologies, which were developed at ISC Konstanz and implemented using processes and equipment that are comparable to those employed in conventional solar cells, such as Al-BSF and PERC. A detailed discussion of the process and history can be found in Chapter 2...@en

Industrial bifacial n-type front and back contact (nFAB) silicon solar cells, consisting of a boron-doped p+ emitter and a phosphorus-doped n+ back surface field (BSF), are known to give good bifaciality, high and stabilized efficiency. One possible approach to further enhance the cell efficiency is to convert conventional passivated emitter and rear totally diffused (PERT) into rear locally diffused (PERL) structure. Herein, bifacial nFAB PERT and PERL cells are fabricated by combining atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG) as doping source and laser processing. For PERL cells, two approaches are studied to locally form phosphorus-doped BSF: 1) laser doping, and 2) laser ablation of a diffusion barrier layer. For ablation approach, an alkaline treatment is introduced immediately after laser process, which leads to the formation of locally textured BSF. Due to this locally textured contact, the resultant fill factor (FF) and series resistance (Rs) loss of the PERL cells are even less than that of the reference PERT cells. As a result, the champion cell of PERL shows a good efficiency of 21.3% with open-circuit voltage (Voc) of 662 mV, short-circuit current density (Jsc) of 39.6 mA cm−2, and a high FF of 81.1%.@en

Industrial bifacial n-type front and back contact (nFAB) silicon solar cells, consisting of a boron-doped p+ emitter and a phosphorus-doped n+ back surface field (BSF), are known to give good bifaciality, high and stabilized efficiency. One possible approach to further enhance the cell efficiency is to convert conventional passivated emitter and rear totally diffused (PERT) into rear locally diffused (PERL) structure. Herein, bifacial nFAB PERT and PERL cells are fabricated by combining atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG) as doping source and laser processing. For PERL cells, two approaches are studied to locally form phosphorus-doped BSF: 1) laser doping, and 2) laser ablation of a diffusion barrier layer. For ablation approach, an alkaline treatment is introduced immediately after laser process, which leads to the formation of locally textured BSF. Due to this locally textured contact, the resultant fill factor (FF) and series resistance (Rs) loss of the PERL cells are even less than that of the reference PERT cells. As a result, the champion cell of PERL shows a good efficiency of 21.3% with open-circuit voltage (Voc) of 662 mV, short-circuit current density (Jsc) of 39.6 mA cm−2, and a high FF of 81.1%.@en

Industrial bifacial n-type front and back contact (nFAB) silicon solar cells, consisting of a boron-doped p+ emitter and a phosphorus-doped n+ back surface field (BSF), are known to give good bifaciality, high and stabilized efficiency. One possible approach to further enhance the cell efficiency is to convert conventional passivated emitter and rear totally diffused (PERT) into rear locally diffused (PERL) structure. Herein, bifacial nFAB PERT and PERL cells are fabricated by combining atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG) as doping source and laser processing. For PERL cells, two approaches are studied to locally form phosphorus-doped BSF: 1) laser doping, and 2) laser ablation of a diffusion barrier layer. For ablation approach, an alkaline treatment is introduced immediately after laser process, which leads to the formation of locally textured BSF. Due to this locally textured contact, the resultant fill factor (FF) and series resistance (Rs) loss of the PERL cells are even less than that of the reference PERT cells. As a result, the champion cell of PERL shows a good efficiency of 21.3% with open-circuit voltage (Voc) of 662 mV, short-circuit current density (Jsc) of 39.6 mA cm−2, and a high FF of 81.1%.@en