18.62%‐Efficiency Binary Organic Solar Cells with a PEDOT₁:PSS_2.80 Buffer Layer

Abstract Binary organic solar cells (OSCs) having a controllable phase‐separated morphology of active layers and simple solution manufacturing are desirable for organic photovoltaic adaptation. However, low hole mobility and an unbalanced hole‐ and electron transport reduce the power conversion efficiency (PCE) of the OSCs. Here, a highly efficient binary OSC with a poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) buffer layer as a hole transport layer (HTL) via using a water‐soluble sulfonate to wrap the PEDOT:PSS core‐shell structures in solutions is reported. The PEDOT₁:PSS_2.80 buffer layers have good merits including i) a smooth, homogeneous, and hydrophilic surface for an intimate contact, ii) a high work function and raised surface potentials with much uniform distributions for an energy band alignment, and iii) a high optical transmittance in the broad spectral region from 400 to 1100 nm along with an improved electrical conductivity. Benefiting from a raised hole mobility and a better charge‐mobility balance, the solution‐processed binary OSCs yielded a high PCE of 18.62%. 18.62% is one of the highest values among these binary OSCs based on the PEDOT:PSS HTLs and PM6:L8‐BO active layers. The PEDOT₁:PSS_2.80 buffer layers are superior to the pristine PEDOT₁:PSS_2.60 buffer layers in terms of raising the OSC efficiency.