Unveiling the Delayed Fluorescence Effects of Triplet-Triplet Annihilation Upconversion on the Photoresponse of Transistor Memory

Delayed fluorescence shows great potential for enhancing the performance of optoelectronic devices. However, the application of triplet-triplet annihilation (TTA) upconversion to phototransistors has remained mysterious. This research investigates the impact of TTA on phototransistor memory by blending poly(1-pyrenemethyl methacrylate) (PPyMA) and tris(2-phenylpyridine)iridium(III) [Ir(ppy)(3)] as a floating gate electret. In the TTA process, PPyMA serves as the emitter, while Ir(ppy)(3) acts as the sensitizer to absorb a longer-wavelength light efficiently. To harness the delayed fluorescence from TTA, 2,7-dioctylbenzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (C8-NDI), whose absorbance perfectly overlaps with the delayed fluorescence and prevents the direct excitation from blue light, is employed as the semiconductor channel layer. A comprehensive optical and morphological analysis is conducted to assess the impact of TTA on photomemory devices and confirm the presence of the TTA process within the system. We compare the effects of typical fluorescence (365 nm) and delayed fluorescence (455 nm) on the photoresponse and memory performance of the device with a PPyMA polymer-based electret and PPyMA/Ir(ppy)(3) as a floating gate. Remarkably, PPyMA/Ir(ppy)(3) exhibits superior stability after ten endurance cycles and a higher memory ratio (>10(5)) over a time duration of 10(4) s, outperforming its counterpart of PPyMA. This observation suggests that excitons generated by TTA have an extended lifetime, facilitating more efficient charge transfer. In conclusion, the delayed fluorescence generated from TTA shows the potential to enhance phototransistor memory. The findings exemplify the effectiveness of delayed fluorescence as a mechanism for endowing phototransistors with additional and exceptional memory capability, thereby underlining the potential for future optoelectronic applications.