Highly efficient dye-sensitized solar cells (DSSCs) with excellent long-term stability were fabricated based on tin(IV) oxide (SnO₂) nanocrystals with tunable morphologies and band energy levels. The nanocrystals were prepared by a facile, fast, and energy-saving microwave-assisted solvothermal reaction. Through variation of the precursor base used during nanocrystal synthesis control over morphology was achieved—precursor metal cations are known to have a strong influence on the growth process of SnO₂ nanostructures. A simple and economic way to prepare semiconducting pastes for photoanodes was devised. The photovoltaic performance of dye-sensitized solar cells based on SnO₂ photoanodes was investigated. A very high power conversion efficiency of up to 3.2%, based on very high V_oc and comparable J_sc and FF [under 1 Sun condition (AM 1.5, 100 mW cm⁻², with shading masks)] was achieved, reporting the highest efficiency value for the cells based on unmodified SnO₂ nanocrystals so far. In order to elucidate the efficient cell behavior, electrochemical properties such as the charge transport in the photoanodes as well as SnO₂/electrolyte interfacial properties were investigated. Uncharacteristically for DSSCs, all devices tested in the present study show an unusual long-term stability under ambient conditions over several weeks.