Presentation Details
| Characterizing Doping and Potential Nonuniformity and Assessing the Effects on High-Efficiency CdSeTe Devices Chun-Sheng Jiang1, Marco Nardone2, Rouin Farshchi3, Carey Reich3, Timothy Nagle3, Dingyuan Lu3, Gang Xiong3, Ed Sartor1, Darius Kuciauskas1, John Mangum1, Steve Johnston1, Lorelle Mansfield1, Matthew Reese1. 1National Laboratory of the Rockies, Golden, CO, USA.2Bowling Green State University, Bowling Green, OH, USA.3First Solar Inc, Santa Clara, CA, USA |
Abstract
Doping and associated electrical potential nonuniformity can be a major issue in thin-film solar cells, inducing inferior Voc. Developing group-V doping combined with Se alloying has been a focus for advancing CdTe photovoltaic technology in recent years. We have performed combined nm-scale characterizations for microelectronic structures using two atomic force microscopy-based nanoelectrical probes, namely Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM). KPFM on the device cross-sections images the distribution of electrical potential drops across the device. SSRM taken on a delaminated front interface and further beveling into the absorber bulk reveals local distributions of doping type and carrier concentration. We applied the characterizations to high-efficiency (22%) As-doped CdSeTe devices. The KPFM potential and SSRM resistance imaging corroborate each other, suggesting that nonuniform doping in the planar direction and the steep resistivity change in the vertical direction as measured by SSRM are associated with the nonuniform potential features observed by KPFM. The high resistivity next to the front interface illustrates a very low doping region and the resistivity drops sharply in ~70 nm into the film bulk, reaching to a carrier concentration in the high 1015/cm3 range. The doping polarity is overall n-type weighted at the interface, and it transitions to p-type at ~30 nm from the interface. We are performing device modeling and efficiency loss analysis, based on the observed doping and potential features and based on a set of characterizations of J-V, QE, C-V, TRPL, PL, and Se profiling, which is expected to unravel the effects of the doping and potential characteristics on the device performance. The approaches of nanoelectrical probe-based characterizations and the device modeling are expected to be applied to a variety of PV technologies.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.