Reduced energetic disorder enables over 14%efficiency in organic solar cells based on completely non-fused-ring donors and acceptors

The large energetic disorder has been regarded as a limitation for the further advance of organic solar cells(OSCs).The intramolecular energetic disorder,which originates from the molecular conformational diversity,is quite different for various non-fused-ring materials and of great importance for the corresponding device performance.In this work,the 2-ethylhexyl on A4T-16,an efficient completely non-fused-ring acceptor,is replaced with the 3-ethylheptyl to obtain a novel acceptor of A4T-3.The out-shifted branching position of 3-ethylheptyl reduces the steric hindrance effect,endowing A4T-3 with a more coplanar structure.As a result,A4T-3 exhibits a lower intramolecular energetic disorder than A4T-16,leading to a more uniform surface-electrostatic potential(ESP)distribution.Therefore,A4T-3 exhibits a smaller barrier for intramolecular electron transport and a higher electron mobility.Meanwhile,the lower ESP endows A4T-3 with reduced non-radiative energy loss when blending with the donor.When using PTVT-T as the donor,the A4T-3-based OSC exhibited comprehensively improved photovoltaic properties in comparison with the A4T-16-based one,delivering a high power conversion efficiency(PCE)of 14.26%.Notably,this is the first report of OSCs where both the donor and the acceptor are completely non-fused-ring materials.According to the material-only cost(MOC)evaluation,the cost of PTVT-T:A4T-3-based device is much lower than that of other high-performance OSCs,revealing the great potential of completely non-fused-ring photoactive materials for application-oriented OSCs.