Enhanced Efficiency and Thermal Stability in All-Polymer p-i-n Organic Photovoltaics With Synergistically Designed Second Polymer Acceptor.

A small amount of a synergistically designed and selenophene-substituted second polymer acceptor, PYISe-BO-OD, was incorporated into the PYIT-OD acceptor layer for enhancing interfacial interactions with the PM6 donor layer, resulting in high-performance and superior thermal stability in all-polymer p-i-n organic photovoltaics. The PM6/PYIT-OD:PYISe-BO-OD (wt. 1:0.1) device displayed a champion power conversion efficiency (PCE) value of 19.1% and a superior T80 (time for PCE = 0.8 PCEonset value at 80°C) value of 3415 h, greatly surpassing the PM6/PYIT-OD device with PCE and T80 values of 16.3% and 937 h, respectively. The PCE and thermal stability improvements resulted from PYISe-BO-OD's optimized intermolecular interactions with both PM6 and PYIT-OD (binding energy value -2.73 and -2.71 eV by density functional theory; Flory-Huggins interaction parameter values of 0.014 and 0.652) that expanded the interfacial i-region, inducing more efficient charge separation and prolonged carrier lifetime. The grazing-incidence wide-angle X-ray scattering results revealed the crystalline coherence length values remained after 2050 h because of the stabilized morphology owing to strong intermolecular interactions of PYISe-BO-OD with PM6 and PYIT-OD. The strategy of incorporating synergistical second polymer acceptor for enhancing both the efficiency and thermal stability of the devices lays the foundation for the realization of p-i-n organic photovoltaic devices.