Revealing the strain-associated physical mechanisms impacting the performance and stability of perovskite solar cells

Identification and investigation of strain at buried interfaces in halide perovskite photovoltaics are crucial for directing research on the performance and stability of perovskite solar cells. In this work, we find a gradual shift in the bandgap of up to 60 meV over a perovskite layer thickness of 300 nm caused by interfacial strain. This graded bandgap is desired from the aspect of device engineering. However, in parallel, the increased defect density causes charge recombination at the buried interface. These two effects compensate each other, resulting in an overall performance improvement under standard one sun illumination. Nevertheless, the disadvantage of enhanced defect density is clearly observed at low light intensities, where the device performance becomes dominated by charge recombination and ion migration. Moreover, the strained interfaces are proven to induce enhanced defect densities, causing significantly accelerated device degradation under illumination as well as in the dark.