In this perspective, we present strategies that foster the expulsion of lead from perovskites to obtain a non-hazardous active material.

their mixture while the halide anion X is usually equal to I − , Br − , Cl − , or a mixture of them, is rewarded as the most promising materials for the next generation photovoltaics. The record power conversion efficiencies (PCEs) have recently reached an unprecedented values of 25.7% on singlejunction small scale devices and 17.9% for areas over 800 cm 2 , [1] which are now close to that of the crystalline silicon solar cells. The origin of such high performances is attributed to the appealing photo-physical properties, including strong optical absorption, tunable bandgap, long carrier lifetimes, high carrier mobilities, and low mid-gap state densities. [2] Therefore, PSCs offer a promi sing prospect for future commercialization. Regardless of the several advantages, PSCs still need to solve several issues before scaling up at the industrial level.One of the major concerns in the PSC community is the operational stability of the devices. Unlike silicon solar cells, which are stable for over 25 years or more, [3] PSCs still lag behind, showing inferior stabilities. In particular, literature on low-temperature-processed devices demonstrated relatively lower stabilities when compared to the high-temperature ones. [4] However, through this review we show that the stability progress is on par with the high-temperature ones. Usually, the low operational stability of the devices is due to a number of factors, including oxygen, moisture, light, temperature, and electrical bias. To overcome the stability issue, identification of the origins of these instabilities is indispensable. However, various reports present results without providing all the parameters that are essential for understanding and comparing. Incomplete data reporting leads to great difficulty in understanding the multiple instabilities. Thanks to the consensus agreement among the PSC community, a robust stability testing protocol has now been employed. [5] Moreover, a template for reporting stability results has now been provided to ensure reliability and a better understanding of the instabilities. Various stability measurements help in identifying the type of instability existing in the devices. These stability measurements include dark storage studies (ISOS-D), light soaking tests (ISOS-L), outdoor stability studies (ISOS-O), thermal cycling in the dark (ISOS-T), light-humidity-thermal cycling (ISOS-LT), lightdark-cycling (ISOS-LC), intrinsic stability testing (ISOS-I), and electrical bias in the dark (ISOS-V). [5] The impending commercialization of perovskite solar cells (PSCs) is plodding despite the booming power conversion efficiencies and high stabilities. Most high-performance, stable PSCs are often processed partially with hightemperature processes, increasing the cost of production and energy payback time. Low-temperature-processed PSCs are crucial as they cut down the expenses lowering the barriers to industrial use. In addition, low-temperatureprocessed methods have a wide range of applicability in flexible devices and for tandem applicatio...

The light soaking phenomenon, in chlorine-based mixed halide perovskite solar cells (PSC) with p-i-n configuration, is studied. Due to light soaking, the solar cells have shown improved open circuit voltage, fill factor (FF), and power conversion efficiency without much change in short circuit current. The devices have returned to their original state upon extended exposure to dark conditions. Capacitance spectroscopy is used to understand the effect of light soaking on various photovoltaic parameters. The observed increase of capacitance value with light soaking in the low frequency region of the capacitance-frequency (C-F) plot is elucidated, as the coupled effect of electronic and ionic processes involving defects. The decrement in the mid-frequency capacitance is attributed to an increase in the width of the depletion region which eventually facilitated the improvement in open circuit voltage and FF. Defect densities, and its distribution in the energy space, are deduced before and after light soaking. The defects density of states of PSC studied are found to reduce from 10 16 to 10 15 eV −1 cm −3 , with a Gaussian distribution, and having a peak energy shift from 0.27 to 0.26 eV.

Perovskite solar cells (PSCs) have different theoretical optimal bandgaps (E g) for outdoor and indoor light harvesting due to the different spectral distributions of the sun and indoor lamps. This work focuses on understanding how both indoor and outdoor photovoltaic (PV) performance of Cs0.05(MA0.17FA0.83)0.95Pb(I1–x Br x )3 PSCs depend on Br– content (x) spanning the whole 0–100% range, not only efficiency but also stability. E g increases linearly with x: E g/eV = 0.75x+1.48. Cells with x = 0.17 delivered the highest efficiency under indoor illumination, which did not correspond to the optimal theoretical bandgap. Via in depth analysis of crystal structure, morphology, and optoelectronic properties, we propose five key parameters and associated threshold values to be surpassed that enable one to achieve indoor efficiencies greater than 25% (1000 lx). First, films should possess average grain sizes greater than 300 nm (i.e., grain sizes > 70% of film thickness) and intergrain spacing ≪ 10 nm. Additionally, On/Off dark current and shunt/series resistance ratios should be higher than 102. Lastly the ratio between current density under indoor illumination and recombination currents in the dark should be >10. The aging rate of cells measured indoors (a fall of 65%) was higher than under 1 sun (41% fall), indicating that device performance is more sensitive to defects arising upon aging when measured under low intensity indoor light. Our investigation provides key parameters that can become a useful tool for researchers aiming to develop improved PSCs for indoor applications.

In the quest for finding non-toxic and stable lead-free perovskite nanocrystals (NCs), bismuth halide perovskites (BHP) have emerged as a promising alternative. This perspective presents an overview, challenges, and future opportunities in BHP NCs.