Perovskite-based tandem photovoltaics (PVs) have emerged as a highly promising technology due to the advancements in single-junction organic-inorganic metal halide perovskite solar cells (PSCs) with a wide range of bandgaps. Tandem PVs, in theory, can surpass the Shockley-Queisser limit for single-junction cells, leading to higher power conversion efficiencies (PCEs). All-perovskite tandem solar cells (2TPT-SCs), specifically two-terminal configurations (2TPT-SCs), are particularly attractive as they combine a wide bandgap (WBG) perovskite top subcell and a narrow-bandgap (NBG) perovskite bottom subcell. Laboratory-scale 2TPT-SCs have demonstrated efficiencies exceeding 23%, even reaching 26.4% in a certified record. However, these achievements relied on non-scalable laboratory techniques. The significant challenge lies in developing scalable fabrication processes and interconnection schemes for 2TPT-solar modules (2TPT-SMs) to transition this technology towards industrial production. While laser-scribed interconnection schemes have been successful for single-junction perovskite modules, the monolithic all-perovskite tandem module presents unique challenges, necessitating inert atmosphere processing and compatibility with the tandem layer stack. Furthermore, scalable deposition methods must replace the current limitations of spin coating which restricts device area. Therefore, the current research focuses on addressing these challenges by developing and implementing scalable fabrication methods for efficient 2TPT-SMs.

Significant progress has been made in achieving high PCEs in laboratory-scale 2TPT-SCs, with efficiencies exceeding 23% reported in several studies. These studies utilized various materials and architectures, focusing on optimizing bandgap engineering, minimizing optical losses, and improving charge carrier transport. For instance, Lin et al. reported a 24.8% efficient all-perovskite tandem cell using a comproportionation approach to suppress Sn(II) oxidation. Xiao et al. achieved a 21.4% efficiency with a 12 cm² active area by using surface-anchoring zwitterionic molecules. However, a significant gap exists in translating these laboratory-scale successes into scalable manufacturing processes. Existing research on scalable thin-film modules typically employs the concept of elongated PSC stripes separated by interconnections formed by three scribing lines. This concept is adapted from other thin-film technologies like perovskite/CIGS, where high geometric fill factors (GFF) have been achieved in single-junction modules. However, applying this to 2TPT-SMs requires overcoming the challenges of inert atmosphere processing and material compatibility with the tandem architecture. Similarly, scalable solution-based methods such as blade coating and slot-die coating have shown promise for single-junction perovskite modules, but their application to 2TPT-SMs requires careful consideration of sequential layer deposition and the prevention of interlayer degradation.

This study focuses on developing and characterizing laser-scribed 2TPT-SMs fabricated exclusively with scalable techniques. The approach involves several key stages: 1. **Reference Device Architecture:** A high-performance p-i-n architecture spin-coated 2TPT-SC served as the baseline. This reference design minimized optical losses and achieved a PCE of up to 23.5% in small-scale devices (0.1 cm² aperture area). The detailed material layers include: * Front electrode: hydrogenated indium oxide (IO:H) * HTL: (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) * WBG perovskite absorber (FA_0.83Cs_0.17Pb(I_0.83Br_0.17)₃; E_g=1.78 eV) * LiF ETL * Fullerene (C₆₀)/SnO₂ recombination layer * ITO (~15 nm) * HTL_bottom: poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) * NBG perovskite absorber (Cs_0.15FA_0.85MA_0.1Sn_0.5Pb_0.5I₃; E_g=1.26 eV) * ETL_bottom: phenyl-C₆₁-butyric acid methyl ester (PCBM)/C₆₀ bathocuproine (BCP) * Back electrode: Cu 2. **High-Throughput Laser Scribing:** A custom-built laser-scribing setup allowed for patterning in an inert atmosphere, preventing oxygen exposure and degradation of the NBG bottom subcell. This process was initially tested on small-scale spin-coated 2TPT-SMs (2.25 cm² aperture area) before being applied to larger modules. 3. **Scalable Module Fabrication:** Larger modules (12.25 cm² aperture area) were fabricated using a combination of blade coating (for solution-processed layers) and vacuum deposition (for evaporated layers). The blade-coating was optimized to prevent degradation of underlying layers, and a vacuum-assisted growth control (VAGC) along with nitrogen gas flow was applied to improve the crystallization of the NBG perovskite layer on the top cell, swiftly extracting the solvents and preventing degradation of the underlying WBG layer. 4. **Characterization:** Various characterization techniques were employed to assess module performance and quality, including current density-voltage (J-V) measurements, electroluminescence (EL) imaging, laser-beam-induced current (LBIC) mapping, photoluminescence (PL) imaging, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and scanning electron microscopy (SEM).

The study successfully demonstrated the fabrication of scalable 2TPT-SMs with high efficiency and good stability. * **High Efficiency:** Spin-coated 2TPT-SMs (2.56 cm² aperture area) achieved a PCE of 22.2% (23.7% active area PCE), with a V_OC of 8.0 V and a fill factor (FF) of 75%. Scalable 2TPT-SMs (12.25 cm² aperture area) exhibited a PCE of 19.1% and stable power output. * **Scalable Fabrication:** The use of blade coating and vacuum deposition enabled the fabrication of 12.25 cm² modules, demonstrating the scalability of the approach. A vacuum-assisted growth control (VAGC) with nitrogen gas flow proved crucial in preventing degradation of the WBG perovskite during the deposition of the NBG perovskite layer. * **Homogeneous Current Collection:** Electroluminescence imaging and LBIC mapping confirmed homogeneous current generation and collection across the entire module area, minimizing losses in V_OC and FF. The losses in V_OC and FF were below 5% in scalable modules and even lower in spin-coated modules. * **Selective Laser Scribing:** ToF-SIMS measurements confirmed the highly selective laser ablation of materials at the interconnection lines, resulting in a high GFF of 94.7% (±0.1%). * **Stability:** The modules exhibited stable power output, maintaining 95% of their initial stable power conversion efficiency (SPCE) during 15 hours of maximum power point (MPP) tracking under continuous AM 1.5G illumination and significant stability at 85°C under inert atmosphere. This stable power output represents a substantial advance in the technological readiness level of all-perovskite tandem photovoltaics compared to spin coated reference devices. The detailed layer structure and optimization of parameters allowed the authors to reach higher efficiency and stability of the modules. Specific improvements included lower parasitic absorption losses in the transparent conducting oxide (TCO) electrode, reduced losses in the hole transport layers (HTLs) of both subcells, and minimized losses in the recombination junction. The percolated Au recombination layer showed better yield compared to the ITO recombination layer despite the increased parasitic absorption losses due to plasmonic losses.

The results of this study address the critical challenge of scaling up high-efficiency 2TPT-SCs to module level, demonstrating the feasibility of achieving high PCEs using industrially relevant fabrication techniques. The achievement of a 19.1% efficiency in a 12.25 cm² module represents a significant advance compared to previous research, bringing all-perovskite tandem photovoltaics closer to commercialization. The high GFF (94.7%) achieved through optimized laser scribing and the homogeneous current collection demonstrated by EL and LBIC imaging underline the effectiveness of the employed fabrication methods. The minimal loss in V_OC and FF between small-area cells and modules points towards the maturity of the module architecture and processes. The study's findings have significant implications for the field of PV technology, highlighting the potential of all-perovskite tandem modules to compete with existing commercial technologies. Future research directions include improving the long-term stability of the modules, further optimizing the module architecture, and developing even more cost-effective scalable fabrication techniques.

This work successfully demonstrated a scalable fabrication route for high-efficiency two-terminal all-perovskite tandem solar modules. The combination of blade coating, vacuum deposition, and optimized laser scribing resulted in modules with a PCE of 19.1% (12.25 cm² aperture area) and excellent stability. The homogeneous current collection and high GFF underscore the effectiveness of the approach. Future research should focus on enhancing the long-term stability of the NBG perovskite, exploring new materials and architectures, and further optimizing the scalable fabrication processes for industrial-level production.

The main limitation of the current study lies in the relatively lower stability of the NBG perovskite bottom subcell compared to the WBG top subcell. Although the modules showed good stability under the tested conditions, further improvements are needed to achieve long-term stability suitable for commercial applications. The slightly lower efficiency of the scalable modules (19.1%) compared to the spin-coated modules (22.2%) may be attributed to the inherent limitations of blade coating, leading to variations in perovskite film morphology and thickness which impacts on current collection. Moreover, the use of a percolated Au layer as a recombination layer increased parasitic absorption losses, providing opportunities for improvements in future designs. Finally, the encapsulation process for certification was done under ambient atmosphere potentially causing some degradation losses.