Ternary Blend Strategy for Achieving High-Efficiency Organic Photovoltaic Devices for Indoor Applications

Monomeric perylene diimide (PDI) small molecules display a high absorption coefficient and crystallinity in solid-state thin films due to strong π-π interactions between the molecules. To take advantage of these exciting properties of PDIs, N,N'-bis(1-ethylpropyl)perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) was mixed with a binary blend of PTB7 and PC₇₁ BM to fabricate an efficient ternary blend, which were in turn used to produce organic photovoltaic (OPV) devices well suited to indoor applications (PTB7=poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}), PC₇₁ BM=[6,6]-phenyl-C₇₁ -butyric acid methyl ester). We varied the PC₇₁ BM/EP-PDI weight ratio to investigate the influence of EP-PDI on the optical, electrical, and morphological properties of the PTB7:PC₇₁ BM:EP-PDI ternary blend. Compared with the reference PTB7:PC₇₁ BM binary blend, the ternary blends showed strong optical absorption in the wavelength range in which the spectra of indoor LED lamps show their strongest peaks. The addition of EP-PDI to the binary blend was found to play an important role in altering the morphology of the blend in such a way as to facilitate charge transport in the resulting ternary blend. Apparently, as a result, the optimal PTB7:PC₇₁ BM:EP-PDI-based inverted OPV device exhibited a power conversion efficiency (PCE) of 15.68 %, a fill factor (FF) of 68.5 %, and short-circuit current density (J_SC ) of 56.7 μA cm^-2 under 500 lx (ca. 0.17 mW cm^-2 ) indoor LED light conditions.