RESUMEN
Solar cells are essentially minority carrier devices, and it is therefore of central importance to understand the pertinent carrier transport processes. Here, we advanced a transport imaging technique to directly visualize the charge motion and collection in the direction of relevant carrier transport and to understand the cell operation and degradation in state-of-the-art cadmium telluride solar cells. We revealed complex carrier transport profiles in the inhomogeneous polycrystalline thin-film solar cell, with the influence of electric junction, interface, recombination, and material composition. The pristine cell showed a unique dual peak in the carrier transport light intensity decay profile, and the dual peak feature disappeared on a degraded cell after light and heat stressing in the lab. The experiments, together with device modeling, suggested that selenium diffusion plays an important role in carrier transport. The work opens a new forum by which to understand the carrier transport and bridge the gap between atomic/nanometer-scale chemical/structural and submicrometer optoelectronic knowledge.
RESUMEN
We present a theory of electric field driven phase transitions that occur via nucleation of needle-shaped, metallic particles. The predictions of this theory have much in common with the observations related to nonphotochemical laser induced nucleation (NPLIN). That connection is rather paradoxical because the final NPLIN products are dielectric crystals. By elaborating on the unique features of field induced transitions and the complexities of liquid systems, we discuss how our theory may provide some insight into the open question of the NPLIN mechanism. A qualitative description of the post nucleation stage and conjectures about the microscopic nature of the metallic particles in liquids are also provided.
