Research And Preparation Of The Low-power, Flexible And Transparent Organic Photoelectric Sensors

Photoelectric sensors have a broad application in wearable medical devices. An organic photoelectric sensor based on the phototransistors(OPTs) structure due to have many advantages, such as flexible structure, low-cost, large-area fabrication, is becoming a hot research topic. Especially, the channel current(Ids) of OPTs can be controlled by adjusting the gate voltage(Vg), and the device has the signal amplification effect, making them have better performance than organic photodiodes(OPDs).The recently reported OPTs have some shortcomings including high-power, poor flexibility, low efficiency of absorption of incident light. In this paper, we attempt to overcome these defects. Here, we focused on the working mechanisms of OPTs and developed a low-power, flexible OPTs based on a heterostructure system, then investigated its electrical properties and the photosensitive performance. We further improved the preparation process and proposed a novel method to prepare a transparent gate electrode, which optimized the structure of OPTs and improved the photon absorption efficiency. At last, we designed transparent OPTs to verify the performance of new electrode. The main contents of this paper include the following aspects:a) Preparation and Comparison of two OPTs with different dielectric layer materials PMMA and PVPA, respectively. We find the threshold voltage(Vth) of the PVPA OPTs is as low as ~-1.0V, more than an order of magnitudes lower compared to PMMA device. In addition, the calculated ratio of photocurrent to dark current up to 100, which as twice as PMMA device. The photoelectric response(R) as high as 1.45A/W. Through the test of photoelectric responsivity for PVPA OPTs, we find that the device maintains a strong linearity consistent with incident light intensity dynamic ranges from 80 n W/cm2 to 80 m W/cm2.b) By further studying the transient response of the PVPA device, we find that the response time is decreases with the increased incident light intensity, the response time as low as 40 ms. We applied the carrier-hopping model to explain this phenomenon: in the lower light intensity condition, the photon-generated carriers first occupy the deep energy level.When increasing the incident light intensity, since the deep energy level has been filled, the carriers will gradually occupy the shallow energy level, which leads to faster response.c) We proposed a novel transparent gate electrode based on silver nanowires. The results showed that the transparent electrode holds about 90% transmittance in a wide wavelength range from 450 nm to 1000 nm.d) Based on the transparent electrode, we firstly proposed a full-transparent OPTs. The device showed a good performance of I-V characteristic curve and a good stability in air. Especially, the device with PDPP2T-TT-OD:PC61BM as the active layer showed a good responsibility for the infrared light. The photoelectric response(R) as high as 1.52A/W. The novel transparent electrode has the potential of replacing traditional metal electrode.