Since the 1760s, modern civilization has significantly enhanced human efficiency and living standards, whereas it heavily depends on fossil fuels for primary energy. The overreliance raises concerns about energy and environmental crises. It prompts the need for novel technologies to address rising global energy demand and reduce CO2 emissions. Photoelectrochemical (PEC) cells emerge as an appealing renewable energy solution that enables simultaneous solar energy harvesting, conversion, and storage. It can produce valuable fuels and chemicals through a solar-driven reaction process involving water splitting or CO2 reduction. Current research on photoelectrochemical CO2 reduction (PEC-CO2R) systems are primarily based on conventional silicon and III-V semiconductors. In addition, noble-metal based cocatalysts are generally required to improve the solar-to-fuel (STF) efficiency. In this thesis, I addressed these challenges by developing two innovative photocathode systems utilizing solution-processed semiconductors - Cu2O and CuIn0.3Ga0.7S2. These photoelectrodes demonstrated benchmark PEC-CO2R performance while utilizing earth-abundant cocatalysts and/or semiconductors. The mechanisms governing the optimization of their performance through surface and electrolyte engineering effects were investigated.