It will be demonstrated the development of a series of conjugated polymers based on the donor-acceptor (D-A) approach consisting of benzodithiophene and quinoxaline derivatives as the electron rich and deficient building block that when employed as electron donor components at organic solar cells exhibit high performance and stability, simultaneously. Moreover, it will be shown how the highest occupied molecular orbital (HOMO) can be precisely control by only an atom change at the side substituents. This allowed for a detailed analysis when matching the energy levels of polymer donors and small molecule acceptors. Therefore, we were able to investigate organic solar cells with highest occupied molecular orbital energy level offsets (ΔEHOMO) between 0 - 300 meV. It will be shown that exciton quenching at negligible ΔEHOMO takes place on timescales approaching the intrinsic exciton lifetimes, drastically limiting external quantum efficiency. This finding it is quantitatively described via the Boltzmann steady-state equilibrium between charge transfer states and excitons and further reveal a long exciton lifetime as a decisive design criterion for maintaining efficient charge generation at negligible ΔEHOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at very small ΔEHOMO.

It will be demonstrated the development of a series of conjugated polymers based on the donor-acceptor (D-A) approach consisting of benzodithiophene and quinoxaline derivatives as the electron rich and deficient building block that when employed as electron donor components at organic solar cells exhibit high performance and stability, simultaneously. Moreover, it will be shown how the highest occupied molecular orbital (HOMO) can be precisely control by only an atom change at the side substituents. This allowed for a detailed analysis when matching the energy levels of polymer donors and small molecule acceptors. Therefore, we were able to investigate organic solar cells with highest occupied molecular orbital energy level offsets (ΔEHOMO) between 0 - 300 meV. It will be shown that exciton quenching at negligible ΔEHOMO takes place on timescales approaching the intrinsic exciton lifetimes, drastically limiting external quantum efficiency. This finding it is quantitatively described via the Boltzmann steady-state equilibrium between charge transfer states and excitons and further reveal a long exciton lifetime as a decisive design criterion for maintaining efficient charge generation at negligible ΔEHOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at very small ΔEHOMO.