Search

Ultra-wide-bandgap (UWBG) materials-based power electronic devices suffer from unexpected and uncertain locations of non-uniformity, and high fields degrade these devices, limiting their lifetimes. It is a challenge to identify the exact locations of breakdown (hot spots), and often destructive processes are used, which are costly, time- consuming, and often not realistic. The work presented here is an attempt to demonstrate a non-destructive and reliable photocurrent spectroscopy technique based on the exciton Franz-Keldysh effect in probing the local electric field (F). By including the excitonic effect in quantitatively modeling the absorption lineshape (and, in turn, photocurrent responsivity), F values are estimated while exploring a wide range of physics. A probe that measures F locally is an extremely useful tool for mapping out the F distribution, performing reliability testing, locating hot and cold spots, validating, or refining electrostatic models, and optimizing device geometry. Analyzing the F-dependent responsivity has shed insight into the contributions of self-trapped excitons and self- trapped holes in − 23 to the photocurrent-production pathway. Polarization- dependent photocurrent spectroscopy is also performed to verify various excitonic transitions, identify the crystallographic axes, and understand their behavior with the applied bias. For solar-blind photodetectors, light polarization could help to make PDs more selective to deep UV wavelengths.

This work aims at demonstrating the concept of utilizing waste heat of Photovoltaic cell by thermoelectric devices. Experiments are performed to study the effect of variation of sun concentration from 0.25 to 1.8 suns (1 sun = 1000 W/m2) on the efficiency of the Photovoltaic cell having 5 cm x 5 cm dimensions. It is found that with the increase of sun intensity from 400 (x0.25) to 1600 W/m2 (x1.6) the photovoltaic cell shows variation of the power output from 0.10 W to 0.25 W. Also, this sun intensity variation resulted in the heating of photovoltaic cell. We measured the top and bottom surface temperatures of the photovoltaic cell. The top surface temperature varied in range from 304.7 K to 380.3 K with increasing solar intensity, while the bottom surface has a lower temperature compared to the top surface varying from 303.85 K to 370.55 K. Thermoelectric devices are attached to the bottom surface of the photovoltaic cell to recover the waste heat from the photovoltaic cell. In order to demonstrate the thermoelectric principle, we have first measured the power output we could fetch through the K type thermocouple junction; the same TC junction we have used to measure the temperature on the bottom surface of photovoltaic cell. At input sun intensity of 1800 W/m2 we have measured the maximum power output of around 0.28 µW from this single thermocouple junction. Finally, a V- type longitudinal thermoelectric device made of multiple TE legs is fabricated and attached at the back surface of the photovoltaic cell to demonstrate the increase of the power output. We have also discussed how increasing in the thermal contact area of the thermocouple device could help in increasing the power output from the PV cell. Also, in this work we have performed full three-dimensional numerical simulation on the hybrid photovoltaic and transverse thermoelectric device with natural air convection using ANSYS to gauge the power generation performance for future research.