Electron/hole blocking layers as ionic blocking layers in perovskite solar cells

Abstract

Theoretical studies of ion migration have thus far focused on migration within the perovskite layer only. This reflected a “hidden” assumption that the electron/hole blocking layers also function as ion blocking. Following experimental evidence, we study the effect of ion migration into the blocking layers and as a case study we compare our simulations to experimental results of device degradation under storage conditions (V = 0, dark), obtained by others. Good agreement is found between the simulated ion accumulation at the electrode interface with the experimental device degradation dynamics. Also, we find that the migration into the blocking layers dominates the effects on the device energy level diagram and that it may also turn the intrinsic perovskites into either p or n type solar cells. Although our simulations do not include the chemistry of degradation, they show two potential mechanisms associated with ion out-diffusion. First, the electron/hole balanced solar cell structure becomes imbalanced (should be reversible). Second, ions reaching the electrode may react with it (i.e. irreversible).