Understanding Materials from the Device's Point of View and Vice Versa

Often one studies the chemical physics of materials with the goal to improve or understand their performance in a device, be it a solar cell or a field effect transistor. However, when we operate and measure the device performance, the device implements a very specific filter on the chemical or physical processes. The device structure and its operation conditions would decide on the relative importance of processes, and not less importantly on how the microscopic properties are being averaged to produce the device’s output. I will demonstrate the above philosophy through examples like:<br/>1) The standard FET operates with the current being a drift current. I will present a device structure where the current is determined by diffusion. Interestingly, the source operates as a pressure hose.<br/>2) The exciton binding energy that organic bulk-heterojunction device “sees” is very different to what one would measure through careful (possibly irrelevant) measurements.<br/>3) Mobility imbalance in solar cells was an important topic 20 years ago. It is time to move on.<br/>4) Perovskite devices have rich electrochemistry. Trying to incorporate it into a device model tends to raise more questions than answers. Should we worry about it?