Highly efficient organic solar cells enabled by suppressing triplet exciton formation and non-radiative recombination.

The high non-radiative energy loss is a bottleneck issue that impedes the improvement of organic solar cells. The formation of triplet exciton is thought to be the main source of the large non-radiative energy loss. Decreasing the rate of back charge transfer is considered as an effective approach to alleviate the relaxation of the charge-transfer state and the triplet exciton generation. Herein, we develops an efficient ternary system based on D18:N3-BO:F-BTA3 by regulating the charge-transfer state disorder and the rate of back charge transfer of the blend. With the addition of F-BTA3, a well-defined morphology with a more condensed molecular packing is obtained. Moreover, a reduced charge-transfer state disorder is demonstrated in the ternary blend, which decreases the rate of back charge transfer as well as the triplet exciton formation, and therefore hinders the non-radiative recombination pathways. Consequently, D18:N3-BO:F-BTA3-based device produces a low non-radiative energy loss of 0.183 eV and a record-high efficiency of 20.25%. This work not only points towards the significant role of the charge-transfer state disorder on the suppression of triplet exciton formation and the non-radiative energy loss, but also provides a valuable insight for enhancing the performance of OSCs.