[TuP3H] H. Flexible materials

[TuP3H-04] Charge-Carrier Recombination in PBDB-T:ITIC Organic Photovoltaic Devices with and without a Processing Additive

〇Yuta Takenaka¹, Takashi Nagase^1,2, Hiroyoshi Naito^2,3,4, Takashi Kobayashi^1,2 (1. Dept. of Physics and Electronics, Graduate School of Eng., Osaka Metropolitan Univ. (Japan), 2. The Res. Inst. for Molecular Electronic Devices, Osaka Metropolitan Univ. (Japan), 3. Dept. of Applied Chemistry, Graduate School of Eng., Osaka Metropolitan Univ. (Japan), 4. Ritsumeikan Semiconductor Application Res. Center, Ritsumeikan Univ. (Japan))

Processing additives are widely used to control the interpenetrating donor/acceptor network to achieve high-efficiency organic photovoltaic (OPV) devices. Here, we investigate the effects of a processing additive, 1,8-diiodooctane (DIO), on charge-carrier recombination using conventional and inverted PBDB-T:ITIC OPV devices processed with and without DIO. Recombination was examined by modulated photocurrent (MPC) and photovoltage (MPV) spectroscopy. An increase in the open-circuit voltage is observed in DIO-processed inverted devices, suggesting suppressed charge-carrier recombination. However, the bimolecular recombination coefficient, evaluated from MPV measurements, remains nearly constant regardless of architecture and additive processing. In contrast, we find that the first-quadrant signal in the Nyquist plot of the MPC response, which has been attributed to Shockley–Read–Hall recombination, disappears in DIO-processed inverted devices. Analysis of the J–V characteristics supports this conclusion. The selective suppression of Shockley–Read–Hall recombination in DIO-processed inverted OPVs is likely due to a previously reported vertical composition gradient in PBDB-T:ITIC, which forms an ITIC-rich region near the transparent electrode, thereby favoring the inverted architecture.