Organic photo-detecting devices (OPDs) and solar cells (OSCs) both rely on thin films containing blends of electron donors and acceptors, sandwiched between transmissive and reflective electrodes. This project aims to significantly enhance the performance of such devices, by understanding and manipulating resonant optical cavity effects implemented in this simple device architecture. By tuning the cavity resonance wavelength within the optical gap of both donor and acceptor, weak absorption of intermolecular charge transfer (CT) states is significantly enhanced, opening up opportunities to extend the absorption window to longer wavelengths. Using recently reported new non-fullerene acceptors, we will fabricate and characterize wavelength selective resonant cavity enhanced OPDs with high external quantum efficiencies and short response times, operating at longer wavelengths (>1200 nm) than the current state-of-the-art OPDs. To improve OSC performance, we will tune the cavity resonance wavelength to the optical absorption peak wavelength of either the strongly absorbing donor or acceptor. This results in strong light-matter effects causing a redshift of the absorption onset. This approach will be exploited to overcome the rather large voltage losses and optical absorption losses in state-of-the-art OSC devices.