For a class of 2D hybrid organic-inorganic perovskite semiconductors based on
π-conjugated organic cations, we predict quantitatively how varying the
organic and inorganic component allows control over the nature, energy and
localization of carrier states in a quantum-well-like fashion. Our
first-principles predictions, based on large-scale hybrid density-functional
theory with spin-orbit coupling, show that the interface between the organic
and inorganic parts within a single hybrid can be modulated systematically,
enabling us to select between different type-I and type-II energy level
alignments. Energy levels, recombination properties and transport behavior of
electrons and holes thus become tunable by choosing specific organic
functionalizations and juxtaposing them with suitable inorganic components