Landscape of n-type cell technologyUsing the TaiyangNews November TOP SOLAR MODULES report as an example, the institute noted that the top 3 modules featuring BC technology offer an efficiency range between 23% and 24.2%. In comparison, HJT module technology boasts an efficiency range of 22.5% to 23.18%, while TOPCon modules deliver an efficiency range of 22.5% to 23%. Furthermore, according to the nPV Book 2023 on crystalline silicon solar cell technology, the successful implementation of the LECO metallization process on the front-side metal contact of TOPCon cells achieved a Voc of more than 735 mV. To realize further technological improvement, development of both-sided passivating contacts, known as the double poly TOPCon structure, started. While some experts were initially pessimistic about the back-contact structure, or ZEBRA 2.0, which has both polarities passivated, the poly TOPCon structure presents challenges, such as the difficulty of achieving selective polysilicon. In contrast, the BC structure is relatively simpler if the necessary technology, such as fast lasers, is available, explained Kopecek.Future of BC technologyPresenting the historical trend in the evolution of revolutionary cell technologies, ISC Konstanz highlighted the incorporation of low-cost Cz-Si cells and PECVD-based AlOx film deposition in p-PERC technology in 2018. This progressed into TOPCon technology following the successful implementation of LECO metallization and ALD-based AlOx deposition by 2024. This trend is expected to shift towards the TBC back-contact structure by 2027, according to ISC Konstanz.Regarding BC technology, the research institute has successfully incorporated cost-effective BC interconnect technology, although work remains on copper screen printing and laser structuring technology. However, the institute remains skeptical about when perovskite tandem technology will become mainstream. In line with the technology evolution, the research institute has a vision of 2027+ for the BC module which will feature a temperature coefficient (Tc) below 0.3%/K and bifaciality of up to 90% as well as more than 25% efficiency.Regarding the commercialization of BC technology, which is based on 3 mainstream IBC concepts with different cell architectures – PERC, nPERT, and TOPCon – LONGi Solar has adopted the POLO IBC structure, the BC version of the PERC cell. In 2019, ISC Konstanz transferred the ZEBRA 1.0 version of BC technology to SPIC, which was equipped with laser structuring technology from DR Laser and the classical stringing method for BC half-cell technology. The polyZEBRA technology, the BC version of the TOPCon cell architecture, has been adopted by AIKO and Maxeon. Meanwhile, several other companies, including LONGi, SPIC, FuturaSun, Valeo Cell, and CARBON, are working to incorporate this promising new technology.Inferences from the latest BC workshopThe German research institute also shared a summary of the recent bifiPV Workshop in Zhuhai, China, and the BCworkshop in Delft. The bifiPV Workshop, organized in collaboration with AIKO and ISC Konstanz, concluded that BC manufacturers will adopt bifacial BC technology, material quality will advance to semiconductor grade, and laser technology, which may also be used in module production, becomes increasingly important. Meanwhile, by 2025, BC module efficiency is expected to reach 25%, with a bifaciality factor of 78%. In addition, LONGi predicted that BC technology will be the next big thing by 2027 or 2028.The key takeaway from the BCworkshop in Delft was that the low breakdown voltage of the BC cell will be a crucial technological feature.
