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We investigate the electrical bias-induced degradation mechanism in non-encapsulated mixed halide perovskite CH3NH3PbI3-xClx solar cells in ambient conditions using spatial and time-resolved electroluminescence (EL) measurements. The analyses of spatially resolved EL images reveal the inhomogeneous distribution of luminescence efficiency of the perovskite layer. A significant decrease of ~ 33% in power conversion efficiency (PCE) from 12.15 to 8.15% is found after applying a bias voltage larger than the open-circuit voltage (Voc) for ~ 60 min in the ambient environment. Our findings show that the combined effects of cation defects (MA+/VMA+) migration and decomposition of the perovskite layer are primarily responsible for degrading EL intensity and the photovoltaic properties. [ABSTRACT FROM AUTHOR]

Migration of ionic defects and energy band diagram of p-i-n device at short circuit and forward bias conditions. [Display omitted] • In perovskite layer, differential ionic distribution causes dynamic electric field. • Ion migration and interfacial recombination are the dominate causes of hysteresis. • Increased charge accumulation/recombination leads to lower Voc. • Passivation of traps by PCBM suppresses hysteresis and improves carrier extraction. Using the transient Sun– V oc measurements it has been demonstrated that not only ion migration but charge accumulation/recombination at perovskite/charge transporting layer interfaces also plays a significant role in the hysteresis of J-V curves in perovskite solar cells. The transient ideality factor was investigated for two different architectures of perovskite devices. The wide range variation of transient ideality-factor implies that different ionic distribution causes change in recombination mechanisms. Owing to the passivation effect induced by PCBM, the iodine ions/vacancies were significantly reduced. These findings indicate the importance of efficient charge transfer and reduction of defects/ion accumulation at interfaces for device stability. [ABSTRACT FROM AUTHOR]

Hybrid organic-inorganic metal halide perovskite solar cells are the fastest growing cost-effective photovoltaic technology because of their solution processability and lightweight properties. However, the poor stability of perovskite materials in presence of moisture is the main hindrance to their outdoor applications. Here, paraffin wax is explored as an encapsulating material for improving the water repellency of perovskite solar cells. For this purpose, the drop of paraffin from a burning candle is placed on the device area composed of methylammonium lead iodide as a perovskite material and doped poly(3-hexylthiophene) as a hole-transporting layer. The encapsulation does not affect the photovoltaic performance of the tested devices in ambient conditions, exhibiting the same performance as in an inert atmosphere. Moreover, the photovoltaic performance of the encapsulated solar cells remains unchanged even after 2160 h under ambient conditions with continuous exposure to the relative humidity in the range of 70–85%. The encapsulation is so robust that the photovoltaic performance of the cells does not change even after immersing the encapsulated cell in water or after heating at 85 °C. This performance of paraffin coating is superior to many reported sealing agents, which are deposited using costly instruments or by multistep processes. Thus, the paraffin exhibits the potential to be used as an alternative low-cost coating material for perovskite solar cells. • Paraffin wax has been explored for encapsulation of perovskite solar cells. • The photovoltaic parameters of the encapsulated perovskite solar cells remain unchanged in relative humidity 70–85% for 90 days. • Even no degradation in performance of encapsulated solar cells after immersion in water. • The performance of paraffin encapsulation is similar to keep the devices in an inert atmosphere. • Paraffin-based materials exhibit the potential to be used as low-cost coating materials for perovskite solar cells. [ABSTRACT FROM AUTHOR]