Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm-2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.
KAUST Repository Item: Exported on 2021-02-19
Acknowledgements: D.B. thanks the Helmholtz Association and Julich Forschungszentrum for financial support via Helmholtz Postdoctoral Fellowship. T.K. acknowledges continuous support from Uwe Rau. A.W. and I.M. thanks EC FP7 Project SC2 (610115), EC FP7 Project ArtESun (604397), and EPSRC Projects EP/G037515/1, EP/M005143/1, T.K. acknowledges support from the DFG (grant KI-1571/2-1).