Improving Photovoltaic Efficiency through Textured TOPCon Structures: A New Milestone

Photovoltaics (PV) has experienced a remarkable and unprecedented growth, transforming the global energy landscape and revolutionizing the way we generate electricity. Photovoltaics, also known as solar PV, is a technology that directly converts sunlight into electricity using semiconductor materials. This technology has become synonymous with renewable energy and has played a pivotal role in the transition towards more sustainable and environmentally friendly energy sources. One of the key drivers behind the remarkable growth of PV has been the increasing awareness of climate change and the urgent need to reduce greenhouse gas emissions. Governments, businesses, and individuals around the world have recognized the importance of transitioning away from fossil fuels and embracing clean energy sources. As a result, there has been a surge in policies and incentives to promote the adoption of solar energy, including feed-in tariffs, tax credits, and renewable energy standards. In recent years, innovations in PV technology have continued to push the boundaries of efficiency and performance. New materials like perovskite solar cells, tandem solar cells, and bifacial panels have shown great promise in improving energy capture and output. Moreover, energy storage solutions have complemented PV systems, enabling the utilization of solar power even when the sun isn’t shining.

Among the various PV technologies, crystalline silicon (c-Si) solar cells have emerged as the predominant choice, capturing over 95% of the market share. However, in order to continue the momentum of growth and meet the ever-increasing energy demands, the PV industry requires continuous technological innovations that push the boundaries of efficiency while keeping manufacturing costs in check. To address these challenges and in a new study published in the peer reviewed Journal Advanced Energy Materials, Dr. Jingming Zheng, He Wei, Dr. Zhiqin Ying, Assistant Professor Xi Yang, Assistant Professor Jiang Sheng, Dr. Zhenhai Yang, Professor Yuheng Zeng, and Professor Jichun Ye at the Zhejiang Provincial Engineering Research Center of Energy Optoelectronic Materials and Devices, affiliated with the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, have made significant strides in advancing the efficiency and viability of perovskite/silicon tandem solar cells (TSCs) through the utilization of textured tunnel oxide passivating contact (TOPCon) structures.

The technological landscape of PV has been evolving at a rapid pace, as is evident from the adoption of crystalline silicon solar cells. Despite reaching a certified efficiency of 26.81%, these single-junction c-Si solar cells are nearing their Shockley-Queisser limits of 29.4%. This prompts researchers to explore new avenues for breaking through the efficiency ceiling, and perovskite/silicon tandem solar cells have become a focal point due to their potential to enhance efficiency and reduce costs. These perovskite/silicon TSCs leverage the complementary characteristics of the two materials to create a tandem structure capable of achieving unprecedented levels of efficiency.

The success story of perovskite/silicon TSCs is a testament to the intricate interplay of material properties, structural designs, and advanced fabrication processes. Rigorous research and innovation have propelled perovskite/silicon TSCs, culminating in a certified world record efficiency of 33.7% achieved by KAUST. Such a leap highlights the importance of strategic material integration and structural optimization in maximizing performance. Optical gain/matching and the suppression of electrical recombination have emerged as critical factors contributing to this swift advancement. Researchers have harnessed strategies like antireflection coatings, impedance-matched intermediate layers, and nano-structured c-Si substrates to minimize reflection losses and parasitic absorption. The latter approach, involving the integration of nano-textured c-Si substrates, has demonstrated an exceptional optical response close to theoretical limits.

The introduction of textured structures, however, presents its own set of challenges. The textured perovskite/silicon TSCs, particularly those utilizing double-textured TOPCon designs, require a delicate balance between maintaining high-quality passivation and suppressing the increase of contact resistances. Achieving this equilibrium involves carefully optimizing SiOx thickness, in-diffusion profiles, and pinhole density. The study conducted by Professor Jichun Ye and his team delves deep into this intricate interplay between passivation, contact properties, and charge-carrier transport mechanisms. Their research reveals that tailoring the annealing processes and radio frequency (RF) powers during SiOx film deposition can yield TOPCon devices with passivation and contact properties comparable to polished counterparts, despite the textured nature of the substrate. The use of high-temperature annealing, in particular, emerges as a powerful tool in modulating in-diffusion profiles and thus, device properties.

The heart of the study lies in understanding the complex charge-carrier transport mechanisms on textured structures. This aspect has been meticulously investigated using electron beam-induced current (EBIC) measurements and numerical simulations. These techniques reveal that charge carriers are more prone to transport through the valleys of the pyramid-textured substrates, where SiOx is thin or absent. This critical insight elucidates the crucial role of the textured structures in enhancing charge-carrier collection efficiency, thereby contributing to the overall performance enhancement of the perovskite/TOPCon tandem solar cells.

The culmination of this research is reflected in the efficiency enhancements achieved in perovskite/TOPCon tandem solar cells. By strategically integrating double-textured TOPCon structures, the authors have achieved an impressive efficiency of 28.49%. This achievement underscores the significance of materials engineering and structural optimization in pushing the boundaries of photovoltaic technology. While this efficiency may not surpass the current world record using different materials, it is essential to note that the authors contributions are substantial within the context of the TOPCon technology platform, providing a solid foundation for future advancements.

In conclusion, the research work conducted by the authors represents a significant step forward in advancing perovskite/silicon tandem solar cell technology. By exploring the delicate balance between passivation, contact properties, and charge-carrier transport mechanisms in textured TOPCon structures, they have demonstrated the viability of achieving impressive efficiency improvements. Study findings not only contributes to the fundamental understanding of these complex devices but also provides a roadmap for further advancements in photovoltaic technology. As the global energy landscape continues to evolve, innovations such as these pave the way for more efficient and sustainable energy solutions.