Tiankai Zhang1,Feng Gao1
Linköping University1
It is commonly believed that perovskite solar cells (pero-SCs) show enhanced stability under day/night cycling due to reported self-healing effect in the dark. However, it is discovered that the operational lifetime of highly efficient FAPbI3 pero-SCs is in fact much shorter under day/night cycling mode, being into question the widely accepted approach to estimate the pero-SCs’ operational lifetime based on continuous mode testing. We reveal the key factor to be the lattice volume change during the operation, an effect which gradually relaxes under the continuous illumination mode but cycles synchronously under the cycling mode. The cycled lattice volume change results in plastic deformation and deep trap accumulation during operation, decreasing the ion migration potential and hence the lifetime under the cycling mode. To address the challenges induced by the synchronously cycled lattice volume, we introduce Ph-Se-Cl to stabilize the perovskite lattice during day/night cycling. As a result, the pero-SCs achieved the certified efficiency of 25.6% and a 10-time improved T80 lifetime under the cycling mode (ISOS-LC-2 suggested protocol) after the modification. Our results uncover the unique degradation mechanism caused by the cycling mode and highlight the necessity of lattice volume fixing to prolong the real working lifetime of pero-SCs.