Postdoc Work: Biophotovoltaic Cell

Plants harvest solar energy in a very efficient way via photosynthesis. Some organisms, such as Rhodobacter sphaeroides, harvest light with internal quantum efficiencies of close to 100 %. By utilizing the reaction centers (RCs) from these organisms, biophotovoltaic cells can produce voltages as high as 0.5V. These devices can potentially give high current density (~500 Am^-2) and be produced at low cost.  They show promise to generate electricity with less than a dollar per kilowatt, which is key to the wide spread use of solar cell technology. Furthermore, the ability of these bio-PVs to absorb light under very low intensity conditions is another advantage. Conventionally a bio-PV is made of an electrode coated with a monolayer of RCs which is located in an electrochemical cell. So far, the overall energy efficiencies have been low mainly due to poor charge transfer between RCs and electrodes.

In this project, we are working towards increasing the efficiency by engineering the electrodes and using genetically modified RCs to enhance their orientation. Up to now, we have successfully deposited a monolayer of well oriented RCs on a carbon electrode which can generate electricity upon illumination. The effect of concentration of ions in the electrolyte on the electrical current and the potential of the cell is studied. In addition, a diffusion based model has been introduced which explains the photoelectric response in this particular type of biophotovoltaic device.

 

PhD Thesis work: Organic Metal-Semiconductor Field-Effect transistor (OMESFET)

Organic semiconductors are the most promising material for ultra-low-cost, flexible and biocompatible electronics. However, state-of-the-art organic transistors are still not ready for those applications. Despite the substantial progress achieved in both the performance and fabrication techniques of conventional organic transistors, called Organic Field-Effect Transistors (OFETs), there are a few serious challenges to need to be overcome, including the necessity of a large supply voltage (~40V) in a printed transistor.

I invented an organic transistor design to tackle this problem.  Instead of the conventional MOS structure, I used a Schottky contact between the gate and channel of the organic transistor.  The device is basically an Organic Metal-Semiconductor Field-effect Transistor (OMESFET) with a structure compatible with printing. Both the simulation and experimental results show low voltage operation (<5V). Its potential applications include organic RFID tags and flexible electronics.

In my thesis I also demonstrated the feasibility of combining the OMESFET and conventional OFET structures to form a dual gate transistor design.  The device’s performance was much better than a single gate transistor with the same dimensions. In contrast to OFETs, dual gate transistors do not need a smooth platform and can be built on rough surfaces, such as those on fabrics. The experimental results have shown that the dual gate transistors are very promising for applications such as wearable electronics.

Stretchable RF microstrip circuits