Impact of the aliphatic side chain length on photovoltaic properties of fullerenes functionalized with 3-(1-indenyl)propionic acid esters

It was shown that the chain length of the aliphatic substituent in the alkyl derivative of 3-(1-indenyl)propionic acid of C60 and C70 fullerenes affects the efficiency of photovoltaic cells with the PTB7-Th:fullerene-derivative bulk heterojunction (BHJ). A series of new C60 and C70 fullerene derivatives containing the n-alkyl ester of 3-(1-indenyl)propionic acid were synthesized using the Diels-Alder reaction. The synthesized fullerene derivatives had aliphatic side chains of 4 to 12 carbon atoms in the ester group. All synthesized compounds were successfully used in the BHJ solar cell, achieving energy conversion efficiencies (PCEs) ranging from 0.8 to 3.9%. We observed an increase in solar cell open-circuit voltage of 30 meV for the 60IPH acceptor material. Long aging measurements of the solar cells with the new fullerene derivatives show long lifetimes for C60 derivatives and shorter for C70. The lifetime significantly depends on the aliphatic chain length. The longest 80% decay period, T80, was about 200 days. 10 Indene C60 and C70 derivatives have been synthesized and characterized, and solar cells fabricated using them gave the best efficiency for hexyl derivatives.