Researchers uncover the hidden chemistry driving gradual reverse-bias degradation in perovskite solar cells

Source Summary

A research team, led by Prof. Michael McGehee at the University of Colorado Boulder, working with groups at Northwestern University, the University of Arizona, the University of Washington and the National Laboratory of the Rockies (NLR, the new name for the National Renewable Energy Laboratory), has identified the mechanism behind the slow degradation of perovskite solar cells under reverse bias — and demonstrated a fix that requires no new materials or equipment. Reverse bias is the electrical condition that arises when part of a panel is shaded while the rest sits in full sunlight. It has long been known to damage perovskite devices, but the picture was incomplete. Current can flow under reverse bias by two routes. Where films contain large defects, electrons rush through those sites and destroy the cell outright - an acute failure mode the same group addressed in an earlier study. The second route persists even in films without such defects: current leaks through by quantum tunnelling, distributed across the whole device, degrading it gradually rather than abruptly. That slower pathway has been far harder to characterize, and existing theories could not explain why some cells degraded so quickly, or why certain architectures proved much more resilient than others.