Graphene-based lateral p−n junction photodiodes play a key role in the field of photodetection due to their inspiring features of broadband spectral response, large operating bandwidth and mechanical flexibility. Compared with the popularly used fluorescent materials, phosphor has much abundant electronic states, and can emit an extra slow phosphorescence under optical excitation stemming from the triplet to singlet state electron transitions. When combined with graphene, the peculiar electronic and optical traits of phosphor may provide a solution to realizing graphene-based rewritable photodetectors.

Here, we report an ultraviolet (UV) rewritable p−n junction photodiode in a configuration of graphene coated with an amorphous phosphor of 4-bromo-1,8-naphthalic anhydride derivative polymer (poly-BrNpA). Under moderate UV irradiation, occurrence of photoisomerization reaction in the poly-BrNpA film leads to its drastically modified optical characteristics and a concurrent n-type doping in the underneath graphene. Meanwhile, the poly-BrNpA film, highly sensitive to water molecules, has a capability of restoring graphene to its initial p-type doping status by means of water adsorption. Based on these findings, a lateral graphene/poly-BrNpA p−n junction photodiode, responsive to visible light at the junction interface, can be written by UV irradiation and then erased via water adsorption. The p−n junction photodiode is rewritable upon such repetitive loops showing repeatable optoelectronic properties. This study provides a new scheme and perspective of making graphene-based rewritable p−n junction photodiodes in a flexible and controllable way, and it may contribute to expanding new families of optoelectronic devices based on two dimensional materials.

Figure Schematic demonstration of the UV rewritable p−n junction photodiode that is erasable by H2O molecule adsorption.

The research was published in “Hao Li, Shubin Su, Chenhui Liang, Ting Zhang, Xuhong An, Meizhen Huang, Haihua Tao*, Xiang Ma, Zhenhua Ni, He Tian and Xianfeng Chen*, UV Rewritable Hybrid Graphene/Phosphor p−n Junction Photodiode, ACS Applied Materials & Interfaces 11, 43351−43358 (2019).”

Link: https://doi.org/10.1021/acsami.9b14461