Saddle-like, π-conjugated, cyclooctatetrathiophene-based, hole-transporting material for perovskite solar cells

A flexible, saddle-like, π-conjugated skeleton composed of four fused thiophene rings forming a cyclooctatetrathiophene (CoTh) with four triphenylamines (CoTh-TTPA) is presented as a hole-transporting material (HTM) for perovskite solar cells. The new HTM shows a bright red color stemming from a direct conjugation between the TPA groups and the central CoTh scaffold. This results in a charge transfer band due to the combination of the weak acceptor moiety, the CoTh unit, and the electron-donating p-methoxytriphenylamine groups. CoTh-TTPA exhibits a suitable highest-occupied molecular orbital (HOMO) level in relation to the valence band edge of the perovskite, which ensures efficient hole extraction at the perovskite/HTM interface. It has been applied as the HTM in combination with a mixed perovskite ([FAPbI3]0.85[MAPbBr3]0.15) and a state-of-the-art triple cation perovskite ([(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08) reaching noticeable light-to-energy conversion efficiencies of 16.3 and 15.9%, respectively. These values are slightly lower than those measured for the benchmark spiro-OMeTAD HTM. The HTM properties have been analyzed by means of photoluminescence and conductivity experiments, which demonstrated a better hole extraction and conductivity for spiro-OMeTAD.

Published in:
Journal of Materials Chemistry C, 22, 6656-6663
Apr 18 2019
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 Record created 2020-06-03, last modified 2020-10-25

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