It is often suggested that the dark leakage current of organic photodiodes is due to extrinsic leakage paths that do not involve the electronic junction. By studying a series of devices, where the acceptor is kept constant (C70) and the donor material is varied, we find a direct correlation between the strength of the sub-gap signature of the charge-transfer states and the leakage current. Attributing the differences in the sub-gap absorption to the donor's sub-gap states suggests that the donor's side of the junction should be made longer, to push the Fermi level at V = 0 towards the acceptor's LUMO, and thus, an optimized value of 800 Pacm−2 at V = −1 V is reported.

Organic-based solar cells have developed for the last three decades. Moving forward generally requires the assistance of useful models that are adapted to currently used materials and device architectures. The least understood part of the charge generation is the first step of the exciton dissociation, and new or refined models are being suggested. However, many of today's questions have been asked before, going back almost an entire century. We have gone to the 1930s and attempted to critically review significant contributions on equal footing. We find that Onsager's and Frenkel's models have a similar foundation but were developed to suit very different materials (ions in solutions vs electrons in semiconductors). The contribution by Braun or the Onsager–Braun model can be considered wrong, yet it was instrumental for the field's development. The community practically ignores one of the most promising models (Arkhipov–Baranovskii). Hot exciton dissociation has many faces due to “hot” being a relative term and/or the heat being stored in different ways (electronic, vibronic, etc.). Entropy considerations are instrumental in simplifying the picture, yet they add no physics compared to the full-3D models. We hope that by emphasizing the physical picture of the various models and the underlying assumptions, one could use them as a stepping stone to the next generation models.

Revisiting the intensity-dependent quantum efficiency (IDQE) technique in the context of non-fullerene acceptors, we find that at forward-bias conditions, the response exhibits what seems to be anomalous behavior that is not consistent with light excitation induced trap filling. Analysis based on the Shockley–Read–Hall model leads to the conclusion that the contacts cause the traps to be completely full in the dark. The role of the light excitation is to half-empty the traps, and thus, the “anomalous” behavior is created. By fitting the IDQE at several bias levels, we find that the trapping is consistent with multiphonon capture by a state close to the middle of the gap. As trap-assisted recombination is a significant loss mechanism, it is essential to fully monitor it for indoor applications as well as to cross the single junction 20% power conversion efficiency limit.

While nonfullerene acceptors based organic photovoltaics reaching high power conversion efficiency, their binding energy is 150–500 meV. Here there is a model considering disorder and entropy that able to quantitatively explain this controversy.