ABSTRACT:

With the growing demand for renewable energy, solar cells have become a key technology for power generation. Achieving higher power conversion efficiency (PCE) is crucial to reducing photovoltaic (PV) costs and accelerating the transition to clean energy. While single-junction solar cells dominate the market, multi-junction tandem cells offer higher efficiency by harnessing a broader spectrum of sunlight. Perovskite/silicon tandem solar cells, with their tunable bandgap and scalable manufacturing potential, have exceeded the Shockley-Queisser limit, reaching PCEs of ~34%.

To push efficiency further, perovskite/perovskite/silicon triple-junction (3-J) tandem solar cells offer a promising solution, theoretically capable of achieving 49.4% PCE. However, fabricating efficient 3-J cells faces challenges, such as the need for stable perovskite materials with bandgaps of ~2.0 eV and ~1.50 eV. The ~2.0 eV perovskite, essential for the top cell, suffers from phase segregation under illumination, reducing its efficiency.

We addressed this by developing a synthetic additive strategy combining potassium thiocyanate (KSCN) and methylammonium iodide (MAI), enhancing the perovskite's stability and performance. This resulted in a top cell open-circuit voltage (Voc) of 3.04 V and a PCE of 26.4% over a 1 cm² area. However, reproducibility was compromised by degradation of the ~1.50 eV perovskite middle layer during processing. By modifying the perovskite with ammonium propionic acid, we improved its stability, enabling 86% retention of the initial PCE after 1,000 hours of damp-heat aging. Incorporating these modifications significantly enhanced the reproducibility and PCE of the 3-J tandem solar cells, achieving a PCE of 28.7% (1 cm² aperture area).

Despite these advances, stringent current-matching requirements still limited reproducibility. To overcome this, we developed a four-terminal (4-T) configuration, eliminating interconnection layers. This led to the first 4-T perovskite/perovskite/silicon 3-J tandem cells, reaching a PCE of 31.5%. These results underscore the potential of 3-J tandem cells while highlighting the need for further advancements in material stability and process compatibility.