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Organic photodiodes (OPDs) have demonstrated unique mechanical properties, such as flexibility and stretchability, and can be used as on-skin conformable photodetectors or imagers, for example, to measure biosignals with high reliability. [1][2][3][4][5] Simultaneously, substantial research has demonstrated OPDs with a high specific detectivity comparable with that of commercial silicon photodiodes (%10 12 -10 13 Jones). [6,7] This most representative metric of OPDs has been improved by both enhancing the photoresponsivity and lowering the dark current. [8][9][10][11][12][13] One simple and effective technique to reduce the dark current regardless of the OPD structure is the careful selection and process optimization of the electron transport layer (ETL). [14][15][16][17] ZnO is a well-known and widely used ETL material for OPDs owing to its low work function, high optical transmittance, and easy processing. [18,19] ZnO ETL can be deposited via sputtering, a method that is adaptable to established commercial OPD fabrication. [20,21] However, its general adoption in OPDs is chiefly promoted by its sol-gel processability at low temperatures. [22] This solution processability enables printability and large-area processing of the ZnO ETL, [23,24] which are important assets of OPDs. Utilizing these materials and process advantages, the ZnO ETL has been widely incorporated into a variety of high-performance OPDs, thereby contributing to lowering the dark current and achieving high detectivity (%10 12 Jones) photodetectors in the ultraviolet (UV), visible, and near-infrared ranges. [25][26][27] In addition to their high optoelectronic performance, the application of OPDs with ZnO ETLs as flexible near-infrared photodetectors and imagers has been reported with demonstrated skin conformability and biosignal measurements. [4,5] Recently, to prepare OPDs for commercialization, their performance stability has become essential, and the stability of the photocurrent and dark current values has become the benchmark in exhibiting such stability. [12,26,[28][29][30][31][32] For instance, a study demonstrated the operation of ultraflexible OPDs with ZnO ETL with air stability for more than 10 days, where the photocurrent changed by less than 1% and the dark current changed by a maximum of 2.5, even without a high-barrier passivation layer. [28] The same OPDs underwent 1000 repetitive bending tests, thereby demonstrating the mechanical stability of the OPDs with only 5% change in the photocurrent and dark current change by a maximum of five times. In addition to storage and mechanical stability, stability with respect to external irradiation is critical, given their wide application as photodetectors. The photocurrent

No abstract

Electronics based on perovskite oxides, a class of materials with unparalleled wealth of physical functionalities, possesses high potential to go beyond the present semiconductor-based technologies. Towards universal and scalable oxide-based electronics, an important milestone is to realise both N- and P-type conduction regions – the two fundamental blocks of most of electronic devices – on the same oxide substrate surface. However, in contrast to the case of conventional semiconductors, the formation of planar PN junctions is highly challenging in oxide materials owing to difficulties in carrier doping. Here, we show that high-mobility PN junctions can be formed on a surface of SrTiO3 (STO), one of the most versatile oxide materials, in a robust and low-cost manner by simply depositing Angstrom-thin metal layers on top of an STO substrate near room temperature. Furthermore, by forming planar N-P-N junctions, we successfully demonstrate a new type of oxide-based tunnelling field effect transistor (TFET), which enables an extremely sharp switching with a subthreshold swing value S ~ 38 mV/dec and a large current ON/OFF ratio of 108. This high-performance FET operation is obtained by a new mechanism where a gate voltage strongly modulates the tunnelling probability through the depletion layers at the PN interfaces, utilising the unique strong nonlinear electric-field dependence of the permittivity of STO. Our simple method for selectively forming P and N-type regions monolithically on STO is potentially applicable to a wide range of oxide-based electronic systems, from single devices to integrated circuits, and even to flexible electronics.