SPLTRAK Abstract Submission
The Profound Influence of Substrate Thermal Resistance on the Photovoltaic Properties of Solution-Processed Cu(In,Ga)Se2
Kyle G Weideman& Rakesh Agrawal
Purdue University, West Lafayette, IN, United States

Decreased material usage and manufacturing costs associated with the solution-processing of thin film PV materials such as Cu(In,Ga)Se2 (CIGS) offer a route towards larger scale PV production and deployment. Unfortunately, recent progression in the power conversion efficiency (PCE) of solution-processed CIGS has been slow, and the normal buildup of understanding through worldwide collaborative research has been hampered by batch to bath and lab to lab irreproducibility.
This work presents a potential solution to these issues by identifying the previously understudied variable of substrate thermal resistance during the high temperature growth step of CIGS fabrication. Subtle changes in transient heat transfer are shown to have a large impact on the final device performance, with identical films processed under nominally the same conditions controllably displaying final device PCE’s from < 5% to >14% through variation of only thermal resistances within the furnace system.  A model demonstrating how transient heat transfer determines the interface quality and current collection is proposed, and use of these ideas is shown to reliably manipulate all relevant PV parameters.
This improved understanding of the high temperature growth step then eliminates a previously unaccounted for variable that hampered globally cohesive property improvement and disguised the true impact of other parameters studied in previous works. This will then open up a new avenue of PV property control that is not only limited to CIGS but should also translate to many other material systems such as Cu(Zn,Sn)Se2 where similar high temperature growth steps involving a liquid flux agent are used.