Ternary blends to achieve well-developed nanoscale morphology in organic bulk heterojunction solar cells

Two alkoxynaphthalene-based conjugated polymers, poly((5,5-E-alpha-((2-thienyl)methylene)-2-thiophene)-alt-2,6-[(1,5-didecyloxy)naphthalene])) (PBTDN) and poly((5,5-E-alpha-((2-thienyl)methylene)-2-thiopheneacetonitrile)-alt-2,6-[(1,5-didecyloxy)naphthalene])) (PBTADN), are used as second electron donor materials in a poly(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b′)dithiophene-2,6-diyl-alt-(4-(2-ethylhexyloyl)-thieno(3,4-b)thiophene))-2,6-diyl):[6,6]-phenyl-C₇₁-butyric acid methyl ester (PBDTTT-C: PC₇₁BM) binary blend for organic ternary solar cells. The PBTADN:PBDTTT-C:PC₇₁BM blends yields complementary absorption spectra as well as a better molecular structure ordering and more balanced charge mobility, which together provided excellent charge transport properties with reduced recombination compared to the PBTDN:PBDTTT-C: PC₇₁BM blends. The optimized PBTADN:PBDTTT-C: PC₇₁BM blend solar cells yield higher fill factor (FF) values and better efficiencies compared to the PBDTTT-C: PC₇₁BM binary blend solar cells. The best photovoltaic performances in the PBTADN:PBDTTT-C:PC₇₁BM blend solar cells are characterized by a current density (J_SC) of 16.3 mAcm⁻², an open circuit voltage (V_OC) of 0.73 V, a FF of 53.3%, and a power conversion efficiency (PCE) of 6.9% under AM1.5G illumination. The use of a processing additive, 3 vol% of 1,3-diiodopropane (DIP), increases the PCEs of the organic ternary solar cells to values as high as 7.2% with a high FF of 59.1%.