Crystalline silicon solar cells currently dominate the global photovoltaic market, and combining them with wide-bandgap perovskite solar cells has successfully pushed power conversion efficiency limits even further. However, creating lightweight and flexible versions of these tandem cells has been severely hindered by mechanical interfacial stress between the silicon bottom cell and the perovskite top cell, which often leads to delamination and device degradation.
Now, a team of researchers from the Shanghai Institute of Microsystem and Information Technology (SIMIT) of the Chinese Academy of Sciences, alongside collaborators from the University of Chinese Academy of Sciences and Southwest Petroleum University, has developed an innovative solution to this structural challenge.
In a study published in ENGINEERING Energy, the researchers demonstrated that reducing both the thickness of the silicon wafer and the size of the surface texturing pyramids significantly improves the wafer's flexural strength. Standard V-shaped valleys between large silicon pyramids act as stress concentration points, making thin wafers prone to cracking under bending. By minimizing these pyramid structures, the stress concentration is alleviated, dramatically enhancing the material's mechanical flexibility.
To achieve this, the team employed a synergistic optimization strategy, using a precisely controlled wet-etching process to fabricate small-sized, high-density, and highly uniform submicron pyramids on ultrathin 55 µm silicon wafers. They identified that an optimal etching duration of 360 seconds produced a dense array of uniformly sized pyramids (ranging from 800 nm to 1.7 µm) that perfectly balanced optical light-trapping capabilities with mechanical stability.
This optimal submicron texture yielded a cascade of device improvements:

• Enhanced Electrical Performance: The optimized texturing improved the minority-carrier lifetime and achieved an excellent implied open-circuit voltage.
• Superior Film Quality: The homogeneous submicron structure facilitated complete infiltration of the perovskite layer, promoting uniform nucleation and isotropic grain growth.
• Reduced Defects: The improved structural quality effectively suppressed non-radiative recombination losses and improved interfacial contact properties.

As a proof of concept, monolithic flexible perovskite/silicon tandem solar cells built upon these uniformly textured 55 µm wafers achieved a remarkable steady-state power conversion efficiency (PCE) of 30.04%. The optimized devices demonstrated stable power output and negligible hysteresis.
This breakthrough provides a highly effective surface engineering strategy to resolve the conflict between optical performance and mechanical stability in thin silicon wafers. The resulting highly efficient and mechanically robust devices hold immense potential for the future of low-cost, lightweight, and flexible photovoltaic applications, including aerospace technology, building-integrated photovoltaics, and wearable electronic devices.
DOI: 10.1007/s11708-026-1070-4