Scalable carbon-based electrodes for hole-transport layer-free perovskite solar cells.

Perovskite solar cells (PSCs) have rapidly reached certified single-junction efficiencies near 26%, but deployment is still limited by operational instability, scale-up challenges, and the cost and complexity of typical device stacks. This dissertation explores a simpler, scalable approach: HTL-free PSCs using low-cost, chemically robust carbon (e.g., carbon black) counter electrodes compatible with low-temperature, solution processing. This work demonstrates how carbon-ink formulation, scalable deposition (blade vs. slot-die), and work-function-tuning additives control film quality, interfacial energetics, and device performance. Carbon inks were developed for both coating methods by systematically varying carbon-to-binder ratio, polymer chemistry, and solvent system. Among the binders screened, ethyl cellulose (EC) in anhydrous isopropyl alcohol (IPA) produced the most stable and homogeneous inks, forming smooth, adherent films with uniform thickness (~8–12 μm). Slot-die coating yielded more homogeneous electrodes with higher conductivity and lower sheet resistance than blade coating. Carbon-only devices reached ~6.5% (blade) and ~7.0% (slot-die) efficiency. To address energy-level mismatch and poor perovskite/carbon contact, NiOₓ was incorporated directly into the carbon matrix. At an optimum loading of 5 wt%, NiOₓ produced more compact films and reduced sheet resistance from ~625 to ~500 Ω sq⁻¹ (blade coating) and to ~445 Ω sq⁻¹ (slot-die coating), with stronger photoluminescence quenching and lower charge-transfer resistance. As a result, efficiencies improved to 8.6% (blade) and 10.5% (slot-die). Overall, this dissertation links ink design, scalable processing, and composite electrode engineering to HTL-free PSC operation, supporting low-cost, large-area carbon-based PSC manufacturing.