Publications

Direct observation of grain boundary PN junction potentials in cigs using photoemission and low energy electron microscopy (PELEEM)

Chan, Calvin C.; Ohta, Taisuke O.; Kellogg, Gary L.; Mansfield, Lorelle; Ramanathan, Kannan; Noufi, Rommel

Spectroscopic microscopies with chemical and electronic structure information have become important tools for understanding the complex structure-property-performance relationships of high performing Cu(In1-xGax)Se2 (CIGS) photovoltaic materials and devices. Here, we describe the application of spectrally resolved photoemission and low-energy electron microscopy (spec-PELEEM) to CIGS. With the ability to map relative electric potentials with high fidelity, a large variation in the built-in pn junction potential was observed at CIGS grain boundaries. In any given 20 μm region, the built-in voltage spanned the range from depletion (∼ 0.5 V) to inversion (∼ 1.4 V). These grain-to-grain variations could explain the electron collection efficiency of CIGS grain boundaries and devices. These results highlight the potential of spec-PELEEM to solve critical structure-property-performance issues facing compound thin-film materials.