Among transparent electrode architectures, TCO/metal/TCO multilayers can deliver optical transparency and electrical conductivity that match or surpass those of single TCO films and ultrathin metal layers. In this work, tin-doped indium oxide (ITO) thin films were first optimized on large-area substrates (156 × 156 mm²) by systematically varying the target-to-substrate distance, sputtering pressure, and applied RF power. We report an optimized 50-nm-thick ITO layer deposited at a target-to-substrate distance of 115 mm, which exhibited a thickness non-uniformity of ∼10%, along with a carrier mobility of 47 cm² V⁻¹ s⁻¹, a carrier concentration of 2.60 × 10²⁰ cm⁻³, and a resistivity of 9.24 × 10⁻⁴ Ω cm. Subsequently, oxide/metal/oxide (OMO) transparent electrode configurations were optimized using the optimized ITO as the oxide layer, investigating different combinations of oxide thickness and metal (Ag and Al) thicknesses. Among the studied structures, we report the ITO/Ag/ITO (25/10/25 nm) stack demonstrated superior performance, achieving a low sheet resistance of 12 Ω sq⁻¹ and a high transmittance of 82.5% at 550 nm. When integrated into front/back-contacted silicon heterojunction (FBC-SHJ) solar cells, the optimized OMO electrode improved device performance compared with the other reference electrodes. With respect to the optimized 50-nm-thick ITO electrode, the ITO/Ag/ITO (25/10/25 nm) structure shows clear improvements in device performance, with increases of 16 mV in V_OC, 0.20 mA cm⁻² in J_SC, and 1.23% in FF. These gains represent an absolute efficiency improvement of 1.00%, leading to a maximum efficiency of 23.20%. Interestingly, when a much thinner Ag layer is used (ITO/Ag/ITO, 25/2/25 nm), the device performance drops noticeably efficiency of 16.20%. We report that increasing the Ag thickness to 10 nm, however, leads to a substantial recovery and enhancement, emphasizing how sensitive device performance is to the thickness of the metallic interlayer.

The monolithic integration of perovskite top cells on textured crystalline silicon affords efficient tandem devices with strong prospects for large-scale applications. Such integration has primarily relied on state-of-the-art recombination junctions, which typically comprise transparent conductive oxides and molecular self-assembled monolayer (SAM) contacts. However, the potential influence of bottom cell nanoroughness, which may vary based on specific processing routes and technologies, has received far less attention. Here, we systematically engineered the top surface nanoroughness of silicon heterojunction solar cells to examine its impact on monolithic perovskite–silicon tandem solar cells. We employed two approaches: (i) varying the thickness of (n)-type hydrogenated nanocrystalline silicon ((n)nc-Si:H) layers or (ii) applying a plasma treatment using a hydrogen and carbon dioxide gas mixture before the deposition of (n)nc-Si:H layers. Both methods enhanced the conductivity and crystallinity of (n)nc-Si:H layers and increased the surface nanoroughness, with plasma treatment enabling the efficient realization of distinct nanoroughness in thin (n)nc-Si:H (15-nm-thick) layers. Our results reveal that the surface nanoroughness imposed by (n)nc-Si:H layers influences the SAM anchoring, leading to increased work function shifts and improved SAM/perovskite interface quality, thereby impacting the overall tandem device performance. Notably, tandem devices incorporating higher-nanoroughness bottom cells achieved increased fill factors, dominating the observed tandem efficiency enhancements, with a peak efficiency of 32.6% enabled by a 30-second-long plasma treatment.