Unraveling the Singlet Fission Effects on Charge Modulations of Organic Phototransistor Memory Devices

Organic phototransistor memory has received significant attention owing to its solution processability and flexibility, and its high transmission speed and low energy consumption with light operation provide a promising future in ultrahigh-density data storage devices. In this study, TIPS-functionalized organic small molecules, 9,10-bis[(triisopropylsilyl)ethynyl]anthracene (TIPS-3), 5,12-bis((triisopropylsilyl)ethynyl)tetracene (TIPS-4), and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-5) were introduced and employed as the photogates, while polystyrene (PS) acted as the insulator in the floating gate electrets of phototransistor memory. The TIPS-functionalized structure enabled acenes to be solution-processable, and PS helped to trap charges efficiently. The devices were photowritten with different kinds of light and were electrically erased with a gate voltage of −60 V for 1 s. TIPS-4 exhibited the best memory performance and photoresponse with a stable current contrast of 105 over 104 s and a large shift in threshold voltage of 50 V to 450 nm light. The outstanding charge-trapping capability of TIPS-4 in the phototransistor memory was attributed to the favorable energy level alignment to the semiconducting layer. Notably, the significant photoresponse was ascribed to the singlet fission to triplet photodynamics of TIPS-4, which showed a delayed exciton lifetime providing enough time for charge transfer to the channel layer. The results of this study provide a design concept on organic small molecules in the floating gate electret.