Kinetics of light-induced degradation in semi-transparent perovskite solar cells

Abstract

Perovskite solar cells (PSCs) have now achieved power conversion efficiencies (PCEs) over 25%, but their long-term stability under illumination and thermal stress is still a major barrier to commercialisation. Herein, we demonstrate the evaluation of light-induced degradation activation energy (Ea) of encapsulated semi-transparent PSCs by using the commonly employed method in crystalline silicon solar cells. Different parameters showed different activation energies where primary degradation is due to increase in series resistance, which also led to reduction in short-circuit current. Open-circuit voltage and shunt resistance also change with different Ea, suggesting the mechanism of the reduction is likely to be due to different reasons. Despite each parameter exhibiting slight variation over time for each temperature, the overall trend converges, indicating that each parameter is likely to be primarily reduced by a single dominant reaction. We also report the main cause of irreversible device degradation is not due to the decomposition of the perovskite layer as confirmed by X-ray diffraction characterisation. Instead, our pole figure map and absorption spectra analysis indicate that a loss of crystal symmetry occurs due to ion migration within the device that induce oxidation of 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD). Our work provides a better understanding through quantification of the degradation processes of encapsulated semi-transparent PSCs over time, which is essential for further progress and development of stable perovskite-Si tandem solar cells.