Efficient ternary organic solar cells enabled by asymmetric nonfullerene electron acceptor with suppressed nonradiative recombination

The open-circuit voltage (Voc) of organic solar cells (OSCs) is still far from the Shockley-Queisser limit due to the large non-radiative voltage loss (Delta Vocnonrad). Reducing energy loss (Eloss) to obtain higher Voc without sacrificing Jsc and FF is the key to achieve further improvement in power conversion efficiency (PCE) of OSCs. In this work, we designed and synthesized a new asymmetric nonfullerene acceptor via a dual asymmetric strategy, named as SN-O. Under the synergistic effect of alkoxy chain and nitrogen atom substitution, the LUMO and HOMO energy levels of SN-O are significantly elevated compared to Y6, allowing SN-O to display a high open-circuit voltage with a reduced nonradiative energy loss (Delta Enonrad = 0.177 eV). The alkoxy side chain of SN-O brings an intramolecular conformational locking effect and the large dipole moment of asymmetric molecules facilitate the aggregation properties in thin films. The good miscibility allows Y6 and SN-O to form alloy acceptor attributing to the similar chemical structures. The addition of SN-O as the third component into the D18:Y6 system showed a significant reduction in the nonradiative energy loss and a favorable blend film morphology, thus improves exciton dissociation, charge transport and collection. Consequently, a high PCE of 18.3% was achieved for D18: Y6:SN-O ternary system with simultaneously enhancement of Voc, Jsc and FF, which is much higher than that of the binary devices.

Automated summary

The open-circuit voltage (Voc) of organic solar cells (OSCs) is limited by the large non-radiative voltage loss (Delta Vocnonrad), which can be reduced by minimizing energy loss (Eloss). In this study, a new asymmetric nonfullerene acceptor, SN-O, was designed and synthesized to achieve higher Voc without sacrificing Jsc and FF. The addition of SN-O into the D18:Y6 system significantly reduced nonradiative energy loss, improved blend film morphology, and enhanced exciton dissociation, charge transport, and collection. As a result, an impressive PCE of 18.3% was achieved for the ternary D18:Y6:SN-O system.