Location

Vivian A. Bull Music Center: Delkin Recital Hall

Subject Area

Physics/Applied Physics

Description

In the search for solar cells with lower manufacturing costs, thin film technology was developed. These thin films are only microns thick and are grown at relatively low temperatures, resulting in films with imperfections known as defects. Defects can lower the solar cell’s efficiency, causing thin film solar cells to have lower efficiencies than their single crystalline counterparts. In order to create more efficient thin film solar cells the physical mechanisms behind the defects need to be investigated by sensitive techniques. Capacitance measurements of solar cells are one such technique, as they are able to detect minute changes in charge in the material. For that reason, capacitance is used in many methods to electrically characterize the solar cell. Standard interpretations of capacitance rely on many assumptions, which, if wrong, can skew the results. In some solar cells where a back contact barrier is suspected, measurements at high forward bias can be used. We have seen that apparent signatures of a back contact barrier in Cu(In,Ga)Se2 may actually be the first signs of a negative contribution to capacitance. This talk will discuss the implications of negative capacitance and its relationship to other electronic characteristics of the device.

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May 6th, 3:00 PM May 6th, 3:30 PM

Capacitance Measurements of CIGS: Searching to Distinguish Defects

Vivian A. Bull Music Center: Delkin Recital Hall

In the search for solar cells with lower manufacturing costs, thin film technology was developed. These thin films are only microns thick and are grown at relatively low temperatures, resulting in films with imperfections known as defects. Defects can lower the solar cell’s efficiency, causing thin film solar cells to have lower efficiencies than their single crystalline counterparts. In order to create more efficient thin film solar cells the physical mechanisms behind the defects need to be investigated by sensitive techniques. Capacitance measurements of solar cells are one such technique, as they are able to detect minute changes in charge in the material. For that reason, capacitance is used in many methods to electrically characterize the solar cell. Standard interpretations of capacitance rely on many assumptions, which, if wrong, can skew the results. In some solar cells where a back contact barrier is suspected, measurements at high forward bias can be used. We have seen that apparent signatures of a back contact barrier in Cu(In,Ga)Se2 may actually be the first signs of a negative contribution to capacitance. This talk will discuss the implications of negative capacitance and its relationship to other electronic characteristics of the device.

 

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