Fast-Grown Interpenetrating Network in Poly(3-hexylthiophene): Methanofullerenes Solar Cells Processed with Additive

With the aim of revealing the role of additives in polymer solar cells, different amounts of 1,8-octanedithiol (OT) were added to the poly(3-hexylthiophene) (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM) blend system in order to observe the transition between systems with and without additive. We found that highly efficient P3HT:PCBM networks can be formed in the very early stage of the spin-coating process when a small amount of additive was added. The carrier mobilities of this fast-grown network were found to be comparable with those processed with solvent annealing. As a result, short circuit current density (Jsc) as high as ∼9 mA cm−2 can be obtained and the fill factor (FF) can reach ∼62%. The power conversion efficiency (PCE), however, is limited by the low open circuit voltage (Voc) of the devices processed with OT. According to the grazing incidence X-ray diffraction data, a much shorter interlayer spacing (d(100) ∼ 15.6−15.7 Å) compared with those processed with different methods is observed in the polymer blends processed with OT, which is likely the reason for the low Voc.