New Nitrogen-Containing Heterocyclic Non-Fullerene Electron Acceptor as Guest in PBDB-T:Y6 Blends for Air-Processed Ternary Organic Solar Cells with Efficiency Approaching 16%

Abstract

A new non-fullerene small-molecule acceptor (NFSMA), designated as TDPT-TBA, is synthesized. This molecule is based on an S,N-heteroacene central core connected to a weakly electron-withdrawing end group, 1,3-diethyl-2-thiobarbituric acid. In these findings, it is suggested that incorporating an sp²-hybridized nitrogen atom into a fused cyclopentadiene framework, rather than utilizing a sp³-hybridized carbon atom, can lead to a more effective NFSMA and potentially enhance the performance of organic solar cells. The TDPT-TBA exhibits an upshifted lowest unoccupied molecular orbital energy level of −3.76 eV when compared to the Y6 acceptor. Additionally, there are complementary absorption spectra between both the polymer Poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′] dithio-phene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T) and Y6. Organic solar cells utilizing the PBDB-T:TDPT-TBA blend achieves a high open-circuit voltage of 0.942 V, yielding a power conversion efficiency (PCE) of 13.72%. When TDPT-TBA is incorporated into a PBDB-T:Y6 binary active layer, the optimized ternary organic solar cells reach a PCE of 16.06%, surpassing the efficiency of the binary PBDB-T:Y6 configuration, which is 13.51%, under identical processing conditions. The increase in PCE can be attributed to several factors, including the utilization of excitons generated in TDPT-TBA via energy transfer to Y6, a longer charge carrier lifetime, shorter charge extraction times, increased crystallinity, and denser stacking distance. These factors collectively contribute to reduced carrier recombination and improved charge transport.