Structural order in organic solar cells is paramount: it reduces energetic disorder, boosts charge and exciton mobilities, and assists exciton splitting. Owing to spatial localization of electronic states, microscopic descriptions of photovoltaic processes tend to overlook the influence of structural features at the mesoscale. Long-range electrostatic interactions nevertheless probe this ordering, making local properties depend on the mesoscopic order. Using a technique developed to address spatially aperiodic excitations in thin films and in bulk, we show how inclusion of mesoscale order resolves the controversy between experimental and theoretical results for the energy-level profile and alignment in a variety of photovoltaic systems, with direct experimental validation. Optimal use of long-range ordering also rationalizes the acceptor-donor-acceptor paradigm for molecular design of donor dyes. We predict open-circuit voltages of planar heterojunction solar cells in excellent agreement with experimental data, based only on crystal structures and interfacial orientation.

eff. Furthermore, the infl uence of the hole transport material in a p-doped hole transport layer and the donor-acceptor mixing ratio on this limit V 0 is found to be negligible. Varying the active material system, the quantitative relation between V 0 and E g eff is found to be identity. A comparison of V 0 in a series of nine different donor-acceptor material combinations opens a pathway to quantitatively determine the ionization potential of a donor material or the electron affi nity of an acceptor material.