Perovskite solar cells are gaining attention as cheaper, high-efficiency alternatives to silicon solar cells, but defects in their thin films hinder charge transport, waste energy and reduce device stability.
One approach to reducing these defects is a passivation treatment, in which simple salts or organic molecules are introduced into the perovskite film so that small molecules or ions bind to defect sites and limit their impact on electrical conduction. However, most existing characterization techniques only examine the film surface or provide average macroscopic measurements, making it difficult to confirm how well different passivation strategies work within the film volume.
Researchers from the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences have now developed a three-dimensional electrical imaging method that directly visualizes how defect passivation works within perovskite layers. The study, published December 31 in the journal Newton, reports that this method can map charge transport throughout the film and link these microscopic features to solar cell performance.
The technique is based on tomographic conductive atomic force microscopy, or TC-AFM, which measures local electrical conductivity as the instrument successively removes ultrathin layers of the perovskite film. By stacking the conductivity data acquired at each depth, the team reconstructs a three-dimensional map of the current distribution and charge transport pathways with nanoscale spatial resolution.
Using TC-AFM, the researchers compared perovskite films processed with different passivation strategies and directly observed changes in their internal electrical behavior. Films without passivation showed widespread regions of low conductivity that hinder charge flow, while bulk passivation reduced these resistive domains in the film, especially along grain boundaries.
Surface passivation produced a different profile, especially improving the conductivity near the upper interface of the film, which is important for integration into complete device architectures. When both bulk and surface passivation were applied together, the films exhibited the most uniform and continuous conductive networks, with the remaining low conductivity zones largely confined to the surface.
“These microscopic electrical characteristics are closely correlated with the resulting solar cell performance, establishing a direct link between 3D charge transport within the film and the overall efficiency of the device,” said Prof. XIAO Chuanxiao, a corresponding author of the study.
By providing a direct three-dimensional view of charge carrier migration in perovskite layers, the new method provides a tool for assessing and refining passivation strategies. The authors report that this approach can guide the rational design of higher quality perovskite materials and support the development of more efficient and stable perovskite solar cells, as well as other thin-film electronic and optoelectronic devices.
Research report:Three-dimensional mapping of electrical behavior in perovskite films using tomographic conductive atomic force microscopy
