The need for renewable and sustainable energy might be a concern for the society if we are not able to provide this energy with concomitant environmental protection and economic competitiveness. A technology which allows exploiting sunlight, water, and CO₂ to produce solar fuels will certainly contribute to high rate of solar energy conversion and reduction of global warming. However, major considerations are paid to the construction of heterogenous junctions & surfaces allowing better charge transport kinetics and selective simulative proceeding of desired products in appropriates ratios. For that reason, design and construction of different types of joined semiconductors systems aiming enhancement of charge carrier excitation, separation and their transport dynamics followed by recognition of their intrinsic limitations and enhanced efficiency towards CO₂ conversion, becomes a priority in terms of global advancement in the field.

Recent advances regarding construction of a such heterojunction, consist of coupling of high photocatalytic activity of Cu₂O towards CO₂ reduction with high stability and electric conductivity of substoichiometric titanium oxide. This approach allowed to convert the CO₂ to methanol with high efficiency and at relatively positive potential of 0.1 V vs RHE. The stable and reproducible photocurrents reached more than 1.2 mA/cm² and were attained at standard conditions. Then, the substoichiometric titanium oxide has been replaced by the WO₃ containing more than bare, oxygen deficiencies. Further, change in its crystal lattice system allowed better stabilization of the overall working system and higher rate of solar energy conversion to CO₂ reduction products. The mechanism which has been pointed as responsible for better charge separation in the junction relied onto indirect charge transfer between components and could be diversified by the content of carbon in the upper layer. Design, construction and performance of those systems will be an objective of this presentation.