Here we endeavor to improve the performance and stability of perovskite and polymer solar cells by improving the functionality of each solar cell layer, individually, and the complete device. We endeavor to perform most processes in air, but the spray coating process may be performed under nitrogen environment, and device packaging under a glove box, to avoid degradation. Solar cells are also fabricated by spin coating, as a reference method. Below lists our ongoing projects:
- a) Solvothermal Carbon Doping of PEDOT:PSS
Improving conductivity of solar cell layers, by solvothermal treatment of multi-walled carbon nanotubes (MWCNT)/PEDOT:PSS and Graphene doped PEDOT:PSS is currently being performed in our lab. Our preliminary results show that the conductivity of PEDOTT:PSS thin films doped with CNTs and Graphene is higher than that of un-doped PEDOTT:PSS thin films. The modified PEDOT:PSS film are being used for the fabrication of polymer and perovskite solar cells to improve the device performance.
- b) Conductivity and Stability Improvement of PEDOT:PSS
PEDOT:PSS itself has low conductivity as an electrode layer and its acid nature which comes from the additional sulfonate group of PSS making the solar cells to degrade fast. Therefore, using a novel idea developed in our lab, we are using long-chain tertiary amine (PEGO) to modify the PEDOT:PSS.
- c) Stability Improvement of Perovskite solar cells:
While perovskite solar cells have reached an efficiency of 17.9% within few years, improving the solar cell stability remains an unraveled problem. Replacing liquid electrolyte in perovskite solar cells with solid state films and using several coating layers has led to an increase in device stability. The thickness of each layer is an important factor to achieve highly stable and efficient solar cells. The most important layer affecting the stability of perovskite solar cell is the Hole Transporting Material (HTM) layer. HTM is used to improve the work function of perovskite solar cells. We are currently attempting to improve the stability of perovskite solar cells using various strategies, such as removing or replacing HTM layer with more stable materials and layers.
- d) Fabrication of Perovskite and Polymer Solar Cells on Vibrating Substrates :
Typically the perovskite precursor solution should make a favorable uniform wetting layer resulting in well distributed and large contact surface between perovskite and scaffold layers. We are currently using a novel approach developed and tested in our lab, i.e., using a vibrating substrate instead of a stationary substrate for controlled crystallization and improved performance of the perovskite layer (Fig. 5).
- e) Thin film field efect transistors :
Given that most thin film devices share similar fabrication routes and functionality We are expanding our activities, and now focus on the fabrication of thin film field effect transistors. Two innovative directions are followed. First, emerging perovskite semiconductors are used as the conducting channel of the transistor. And secondly, our developed imposed ultrasonic substrate vibration method is employed to improve the mobility and charge density of the perovskite layer.
- f) Fluid mechanics and heat transfer of thin liquid films :
The group also works on fluid mechanics and heat transfer aspects of thin liquid films We have developed a theory that explains how imposed ultrasonic vibration affects the stability and mixing of thin liquid films of solutions. It is observed that the imposed vibration even though tends to make the liquid film unstable, it causes mixing of precursor solutions, thus improves the functionality of ensuing thin solid films.
- g) Other areas of fluid-thermal sciences :
The group also works on general area Of modeling of liquid atomization and sprays in various applications, such as jet in cross flow and spray coating.
Figure 5: Controlling crystallization of perovskite layer using imposed ultrasonic vibration on the substrate.