Self-assembled graphene/BUBD-1 hybrids for ultrasensitive organic phototransistors

Organic molecules have been attracting intense attention as promising candidates in future large-area, low-manufacturing-cost, and flexible optoelectronic devices. However, limited by their short exciton diffusion length, low mobility, and poor crystallinity, the fabrication of high-performance photodetectors faces severe challenges. Herein, using graphene as a growth substrate, a highly ordered BUBD-1 molecular packing was directly assembled employing conventional thermal evaporation. A sensitive phototransistor covering the UV-visible range (295-658 nm) was demonstrated based on this self-assembled graphene/BUBD-1 organic hybrid. The strong light-matter interaction of organic molecules and efficient interfacial charge transfer enabled a high responsivity of similar to 10(6) A W-1 and reasonable specific detectivity of >10(12) cm Hz(1/2) W-1. Interestingly, the separation and recombination processes of photogenerated electron-hole pairs were highly gate-tunable, and the fastest rise/decay time of 0.33/0.49 ms was simultaneously achieved at V-G = -60 V. The charge transfer that dominated the rise time was limited by two elements: interfacial electric field and carrier density in graphene. For the annihilation of photogenerated carriers, indirect recombination centers in the organic molecular layer and interfacial potential barrier height play a decisive role in the decay time. Our results open up a new avenue for constructing large-scale hybrid films by simple direct growth and also provide some insights into interfacial photogenerated carrier dynamics for electronic applications.