Each p-n junction generates electric current from a distinct wavelength of incoming sunlight, so the more junctions, the higher the efficiency.
Conventional single-junction designs have a theoretical efficiency ceiling of 34%. Multi-junction cells, assuming no limit to the number of interfaces, could reach efficiencies of 87% under highly concentrated sunlight.
Best lab results for traditional PV cells have shown efficiencies around 25%, whereas for multi-junction cells, the efficiency is pushing towards double that figure.
