Method for electrical-structural correlation in isolated CdTe/CdS islands

Industrial activity in the last three years has driven efficiencies of CdTe devices to above 20%. Most of the improvements in efficiency have come from enhancements in short circuit current, while the open circuit voltage (Voc) has remained stagnant. High Voc's have been attributed to longer lifetimes and correlated to defect reduction. Recent work has targeted the understanding of defects in polycrystalline films and their association to electrical performance. However, these approaches do not prevent the formation of defects and cannot deconvolute effects caused by the various types of defects. Our approach uses novel electrically isolated islands created by selective growth in masked substrates. This paper shows results on the growth and the characterization of micro and nano CdTe grains on indexed substrates. Several islands were characterized with SEM, EBSD, AFM and prepared for TEM analysis. Polycrystalline films with interconnected grains showed no difference regarding electrical activity among the grains. In contrast, isolated nano-islands had exponential or linear behaviors from grain to grain. The differences were determined by their own structure and not by surrounding CdTe grains. This technique can be advantageous to decouple defects and to understand the electrical-structural correlation in thin film solar cells.