During the 1970-2001 window, the field coalesced around engineering interfaces to promote charge separation across diverse solar cell platforms. A central pattern involved blending conjugated polymers with fullerene derivatives to create internal donor–acceptor networks that dramatically boost carrier collection and initial power conversion in polymer solar cells, signaling the rise of bulk-heterojunction concepts. Parallel efforts in dye-sensitized and semiconductor-based devices emphasized scalable, low-cost architectures, effective sensitization, and solid-state operation, underpinned by careful control of interfacial energetics and transport pathways. Collectively, the period saw a shift toward techniques and material strategies that foreground interfacial chemistry as a driver of device efficiency and practicality, foreshadowing future integration of organic and inorganic components.