New efficient (thio)acetalized fullerene monoadducts for organic solar cells: characterization based on solubility, mobility balance, and dark current

Abstract

We report a systematic study of organic photovoltaic cells using novel spiro-acetalized and (thio)acetalized [60]fullerene monoadducts bearing five- to seven-membered rings. One of these compounds had power-conversion efficiencies of 5.8% with PTB7 and 4.0% with poly(3-hexylthiophene); the latter is comparable to that of the commonly used [6,6]-phenyl-C₆₁-butyric acid methyl ester. We investigated the precise factor that governs the device performance by examining the solubility, space-charge-limited current mobility balance of holes and electrons, morphology, and dark current. Single-crystal X-ray diffraction highlighted the key role of compact and flexible spiro ring folding in the rim space in fullerene packing.