Anomalous enhancement by alkylamine of the dye-sensitized solar cells using TEMPO redox

- Aging enhanced the performance of DSCs using TEMPO redox.
- Ru-DSCs are compatible with TEMPO redox.
- Alkylamine species are effective additives for DSCs.

It has been believed that the TEMPO redox cannot be used for the dye-sensitized solar cells (DSCs) using a ruthenium dye as a sensitizer. However, we found that the photovoltaic performance of DSCs was gradually improved just by keeping them in dark, and it took more than 3 weeks until the performance was saturated. We identified the reason for it; 2,2,6,6-tetramethylpiperidine (TMP) molecule, which was generated during the aging, prevented the reverse charge transfer. This was caused by the molecular interaction of TMP either with the ruthenium dyes or TEMPO redox or both. We found that the freshly prepared DSCs with a ruthenium dye can give a photovoltaic performance just by adding the piperidine additives. Furthermore, we found that not only heterocyclic amine molecules but also alkylamine molecules which do not include the ring structure show the similar effect. This result will pave the way for a novel interfacial control for the charge transfer.

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