Recoverable degradation of FAPbBr3 perovskite solar cells under reverse-bias: A combined electro-optical investigation

Reverse-bias stability in PV devices is critical to guarantee adequate reliability during sporadic shading instances or when deliberately applying reverse-bias in photodetection applications. Testing reverse-bias stability on PSCs is crucial in providing characterizing insights both into the current state and performance of such devices and also towards their iterative improvement. This paper describes reverse-bias stability testing of semi-transparent FAPbBr3 perovskite solar cells. Stability against reverse-bias was extensively evaluated through both reverse-bias step-stress (RBSS) tests and constant-bias stress (CBS) tests at different voltage bias intensities. During a series of 10 ks tests, cells were revealed to be stable when operated down to −1.5 V (corresponding to approximately 20 % of the breakdown voltage threshold), whereas at −3 V the observed degradation mainly consists in a decrease in open-circuit voltage (from ∼1.5 ÷ 1.6 V to as low as 0.3 V) and parallel resistance (from ∼108 Ω to as low as ∼102 Ω), occurring after ∼100 s; a complete recovery is observed, if cells are left in resting conditions after removing the reverse-bias. The observed degradation is ascribed to a temporary shunt-like mechanism, triggered by ion and vacancy displacement and relocation, which causes a drastic energy-band distortion and internal potential compensation. Additional open-circuit voltage decay (OCVD) testing before and after stress reinforces this hypothesis. Reverse-bias step-stress testing until failure confirms that the mechanism occurs across the whole cell, leading to reverse-current magnitudes of over 300 mA/cm2.