Organic photovoltaics (OPVs) promise cheap and flexible solar energy. Whereas light generates free charges in silicon photovoltaics, excitons are normally formed in organic semiconductors due to their low dielectric constants, and require molecular heterojunctions to split into charges. Recent record efficiency OPVs utilise the small molecule, Y6, and its analogues, which – unlike previous organic semiconductors – have low band-gaps and high dielectric constants. We show that, in Y6 films, these factors lead to intrinsic free charge generation without a heterojunction. Intensity-dependent spectroscopy reveals that 60–90% of excitons form free charges at AM1.5 light intensity. Bimolecular recombination, and hole traps constrain single component Y6 photovoltaics to low efficiencies, but recombination is reduced by small quantities of donor. Quantum-chemical calculations reveal strong coupling between exciton and CT states, and an intermolecular polarisation pattern that drives exciton dissociation. Our results challenge how current OPVs operate, and renew the possibility of efficient single-component OPVs.

The exceptional optoelectronic properties of metal halide perovskites have been illuminated by extensive spectroscopic studies. Recent measurements suggest strong photoinduced refractive index changes in these materials, which influence their functionality and obscure access to photoinduced extinction spectra from transient absorption spectroscopy, but such photorefractive effects are difficult to measure and model. Here, we use white light pulse interferometryan experimentally straightforward adaptation of transient absorption spectrosco-pyto directly probe photoinduced refractive index changes in CsPbBr 3 films and nanocrystals on ultrafast time scales. Strong photoinduced refractive index changes are spectrally resolved and used to access extinction spectra, and these intrinsic optical parameters are then used to directly resolve more accurate photoexcited carrier temperatures and bandgap renormalization, resolving ambiguities in the present literature. As well as understanding the intrinsic photoresponse of semiconductors, quantifying photoinduced refractive effects will be valuable for designing photonic devices including switches, lasers, and concentrating photovoltaics.