Bias-free photoinduced threshold-voltage memory effect in TIPS-pentacene organic phototransistors

The bias-free photoinduced memory effect in TIPS-pentacene organic phototransistors was investigated by transfer-characteristic and surface-potential measurements. A positive threshold-voltage shift induced by 400 nm light irradiation persisted after the light was turned off, demonstrating a photoinduced memory effect. A positive threshold-voltage shift was also observed under bias-free conditions, indicating that the effect cannot be explained solely by field-assisted charge separation under an externally applied bias. Surface-potential measurements, together with comparisons between untreated and phenyltrichlorosilane (PTS)-treated devices, suggest that hydroxyl groups on the SiO₂ surface serve as electron-trapping sites, leading to persistent interfacial charge trapping responsible for the bias-free photoinduced memory effect.