Low cost and efficient solar cells are vital for achieving carbon neutrality goals. Silicon heterojunction (SHJ) solar cells have become a research hotspot in the photovoltaic field due to their high conversion efficiency and low temperature coefficient.  Presently, power conversion efficiency of SHJ solar cells has reached over 26%. However, the shortage of indium resources used to prepare indium-based transparent electrodes (TEs) and expensive silver metal electrodes have limited their large-scale applications in the future. Therefore, in order to achieve the target production of sustainable multi-terawatt scale manufacturing, it is necessary to largely reduce the consumption of indium-based TEs and silver.

Based on the above issues, reducing the consumption of indium and silver has become a research focus. One method is to replace screen printed silver electrodes with electroplated copper electrodes, achieving a cost reduction effect of "replacing silver with copper". Another approach is to find other non-indium TE alternatives to indium-based TE to reduce the use of indium. Zinc oxides (ZnO), such as aluminium doped (AZO) and boron doped (BZO), has been selected to partially replace indium based TEs. However, if an electroplating process is used to prepare electrodes, the acid and alkali resistance of TEs must be considered, as the electroplating process requires immersing the cell in a strong acid electroplating solution and a strong alkali stripping solution. Unfortunately, ZnO-based materials developed so far are not very resistant to corrosion, while tin oxide (SnO_x) based materials have better chemical stability. Undoped SnO_x thin film fabricated by solution and atom layer deposition has been widely investigated for perovskite, silicon and perovskite/silicon tandem solar cells as selective carrier transporting layer or anti-ion-bombardment buffer layer, respectively. Up to know, there are no reports in solar cells as TEs.

In this work, undoped SnO_x thin films are prepared at room temperature using commercially compatible sputtering deposition technique, which is widely used in SHJ solar cells. By adjusting the pressure, the ratio of argon to oxygen and the power mode, high-quality thin films with excellent optoelectronic properties were obtained. We replaced the front TEs in SHJ solar cells with SnO_x films and achieved an efficiency of 24.91%. By combining hydrogenated transition metal doped indium oxide (IMO:H) and SnO_x thin films as bilayer transparent conductive oxides, the contact resistance to a-Si:H(n) is reduced, thereby increasing the fill factor and further improving the performance of SHJ solar cells. In addition, it was also verified that IMO:H+SnO_x bilayer films have good resistance to acid and alkali corrosion, enabling SHJ solar cells to maintain good performance stability even during the electroplating process. Finally, the certification efficiency is as high as 25.94% (with a total area of 274.4 cm²) achieved by applying IMO:H+SnO_x bilayer films as the front and rear TEs combined with electroplated copper electrodes.

This work titled “Silicon solar cell with undoped tin oxide transparent electrode” was published in the latest volume of Nature Energy journal (https://www.nature.com/articles/s41560-023-01331-7).