Three graduate students from the Purdue ChE Solar group led by Professor Agrawal performed commendably at the 39th Photovoltaic Specialists Conference held in Tampa, Fl, June 16-21, 2013

Charles Hages was nominated for the Best Poster Award in the Device Properties and Manufacturing Issues session for the poster titled “Device Comparison of Champion Nanocrystal-Ink based CZTSSe and CIGSSe Solar Cells: Capacitance Spectroscopy”

Authors: Charles J Hages, Nathaniel J Carter, James Moore, Steven M McLeod, Caleb K Miskin, Chinmay Joglekar, Mark S. Lundstrom, Rakesh Agrawal

Abstract: Capacitance spectroscopy has been used to compare charge carrier and defect properties of champion nanocrystal-ink based CZTSSe and CIGSSe solar cells, with achievable efficiencies reported here of 9.15% and 14.2%, respectively.  Two defect levels as well as deeper defects in the absorber have been identified for both materials; however, differences in energy level, frequency/temperature response, and contribution to bulk conductivity from these defects have been characterized for the different materials.  Due to these differences, contributions to the free carrier density have been associated with a single defect for CIGSSe, while associated with two defects in CZTSSe.  Additionally, carrier freeze-out at low temperatures has been identified for both devices, contributing to increasing series resistance at low temperatures as determined from the bulk conductivity.

Bryce Walker was nominated for the Best Poster Award in the Absorber Formation and Characterization Session for the poster titled “CZTSe Devices Fabricated From CZTSSe Nanoparticles”

Authors: Bryce C Walker, Bethlehem G Negash, Stephen M Szczepaniak, Kevin W Brew, Rakesh Agrawal

Abstract: To understand and control the growth paths of kesterite based CZTSe films as prepared from homogenous kesterite nanoparticles we investigate films prepared from different chalcogenide ratios in the initial nanoparticles.  To do so we introduce a new method for producing homogenous kesterite nanocrystals with controlled ratios of sulfur and selenium.  The route is proven with the complex quaternary kesterite system based off of CZTS, and it is possible that the path can be readily applied to both material systems that are simpler in structure and potentially more complex.  When compared to going only from pure sulfide nanocrystals to selenide films, the mixed chalcogen nanoparticles formed show beneficial performance when sintered into final devices, which is perhaps the most important aspect of the work for the realization of commercially scalable kesterite solar cells.  Device performance has shown a total area power conversion efficiency of 8.2% without anti-reflective coating. Even particles that are initially 78% selenide perform well upon selenization.  This finding is contrary to the previous hypothesis and points to a different mechanism for the formation of densified grains.

Nathan Carter was a finalist for the Best Student Presentation Award in the Chalcogenide Thin Film Solar Cells and Related Materials Area for the talk titled “Analysis of Temperature-Dependent Current-Voltage Characteristics for CIGSSe and CZTSSe Thin Film Solar Cells from Nanocrystal Inks”

Authors: Nathaniel J. Carter, Charles J. Hages1, James E. Moore, Steven M. McLeod1, Caleb K. Miskin, Chinmay Joglekar1, Mark S. Lundstrom, Rakesh Agrawal

Abstract: Thin film solar cells with CIGSSe and CZTSSe absorber layers fabricated from nanocrystal inks represent economically scalable technologies for alternative sources of energy.  Although these two materials share similar properties important to functioning as a photovoltaic absorber, lab scale CIGSSe devices have achieved power conversion efficiencies 1.5 to 2 times higher than their CZTSSe counterparts. In the current work, CIGSSe and CZTSSe devices similarly processed from nanocrystal inks and exhibiting efficiencies of 14.2% and 9.15%, respectively, are characterized by temperature-dependent current-voltage (IVT) analysis to reveal barriers to current collection inhibiting CZTSSe device performance compared to CIGSSe.