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Understanding device instability mechanisms in halide perovskite solar cells (PSCs) is the key aspect to achieve a breakthrough in photovoltaics. One of the puzzling questions in this regard is electrical bias-dependent degradation of PSCs. Several mechanisms have been suggested to explain the effect, but none are sufficient to embrace all observations. Bias-dependent degradation has been observed in several types of previously developed solar cells, and was attributed to a variety of underlying mechanisms. For example, extrinsic and intrinsic migration of mobile ionic species, which are widely believed to be one of the main reasons for PSC instability, were known to instigate degradation of CdTe and CI(G)S-based photovoltaics. Yet, the stability of these types of solar cells was greatly improved by rational design and currently meets the requirements of in-field applications. In this paper we review the progress in the understanding of bias-dependent instabilities in different photovoltaic technologies (including perovskites) and discuss what lessons can be learned to improve the PSC stability.

Degradation of perovskite solar cells is shown to be partly reversible in the dark, which significantly affects the lifetime of the cell under operational conditions. In this contribution, complex interplay between reversible and irreversible degradation is discussed on the basis of indoor illumination-recovery experiments and outdoor exposure to natural diurnal cycle. We demonstrate that both photodegradation and subsequent recovery processes are strongly affected by the electrical bias condition during the aging. Light-induced ion migration and metastable traps formation with different dominance under different biases and at different degradation stages might explain observed features.

We report on utilizing free-standing hybrid perylenediimide/carbon nanotube (PDI/CNT) films fabricated in air as back contacts for fully inorganic perovskite solar cells (glass/FTO/dense TiO2/mesoporous TiO2/CsPbBr3/back electrode). The back contact electrode connection is performed by film transfer rather than by vacuum deposition or by wet processing, allowing the formation of highly homogeneous contacts under ambient conditions. The use of this novel electrode in solar cells based on CsPbBr3 resulted in efficiency of 5.8% without a hole transporting layer; it is significantly improved in comparison to the reference cells with standard gold electrodes. Overall device fabrication can be performed on air, using inexpensive processing methods. The hybrid film electrodes dramatically improve the cell photo-stability under ambient conditions and under real-life operating conditions outdoors. The champion unencapsulated device demonstrated less than 30% efficiency loss over 6 weeks of outdoor aging in Negev desert conditions. The CNT/PDI electrodes offer the combination of fabrication simplicity, unique contacting approach, high efficiency and good operational stability for perovskite photovoltaics.

The operational stability of perovskite solar cells (PSCs) remains a limiting factor in their commercial implementation. We studied the long-term outdoor stability of ITO/SnO2/Cs0.05((CH3NH3)0.15(CH(NH2)2)0.85)0.95PbI2.55Br0.45/spiro-OMeTAD/Au cells, as well as the dynamics of their degradation, under simulated sunlight indoors and their recovery in the dark. The extent of overall degradation was found to depend on processes occurring both under illumination and in the dark, i.e., during the daytime and nighttime, with the dynamics varying with cell aging. Full recovery of efficiency in the dark was observed for cells at early degradation stages. Further cell degradation resulted in recovery times much longer than one night, appearing as irreversible degradation under real operational conditions. At later degradation stages, very different dynamics were observed: short-circuit current density and fill factor exhibited a pronounced drop upon light turn-off but strong improvement under subsequent illumination. The interplay of reversible and irreversible degradation processes with different recovery dynamics was demonstrated to result in changes in the cell's diurnal PCE dependence during its operational lifespan under real sunlight conditions.

The development of hybrid organic–inorganic halide perovskite solar cells (PSCs) that combine high performance and operational stability is vital for implementing this technology. Recently, reversible improvement and degradation of PSC efficiency have been reported under illumination–darkness cycling. Quantifying the performance and stability of cells exhibiting significant diurnal performance variations is challenging. We report the outdoor stability measurements of two types of devices showing either reversible photo-degradation or reversible efficiency improvement under sunlight. Instead of the initial (or stabilized) efficiency and T80 as the figures of merit for the performance and stability of such devices, we propose using the value of the energy output generated during the first day of exposure and the time needed to reach its 20% drop, respectively. The latter accounts for both the long-term irreversible degradation and the reversible diurnal efficiency variation and does not depend on the type of process prevailing in a given perovskite cell., This work was supported by the European Commission’s StableNextSol COST Action MP1307.

Degradation rates in perovskite solar cells (PSCs) were previously shown to be bias dependent; however, little is known about the mechanisms and driving factors that account for such degradation. Herein, stability studies under concentrated sunlight are demonstrated as a powerful experimental methodology to investigate bias-dependent PSC degradation mechanisms. Stress testing of encapsulated PSCs’ stability shows that light intensity is more significant than the illumination dose for PSC degradation under short-circuit (SC) conditions, whereas the dose is the determining factor under open-circuit (OC) stressing. This indicates that different degradation mechanisms are dominant under different bias conditions. It is postulated that degradation at SC biasing is dominated by ion migration, facilitated by photogenerated defects. Degradation at OC biasing can be explained by photogenerated radicals acting as nonradiative recombination centers (charge traps), which are created via reactions with accumulated charge carriers. Trap formation upon OC biasing is in accordance with degradation of photoluminescence and OC voltage (VOC) observed under this stress. A combination of multiple mechanisms, all with reduced driving forces compared with OC /SC biasing, explains degradation at maximum power point biasing. Understanding the bias effect on PSC stability can elucidate the underlying degradation mechanisms and lead to routes to reduce them.

Polyaniline -Polyisoprene composites were prepared by chemical method. The Polyaniline particles were of nanometer size. The characterization of the PANI-Polyisoprene composite were done by UV-visible spectrometer, Dynamic light scattering and Keithly source meter. The size of the polyaniline particles was found to be 23.29 nm. The electrical properties of the sandwich structure using ITO-Polyisoprene-PANI-Al indicated that the composite can find application in microelectronics.