Fractional deviations in precursor stoichiometry dictate the properties, performance and stability of perovskite photovoltaic devices

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159

167

Transferring the high power conversion efficiencies (PCEs) of spin‐coated perovskite solar cells (PSCs) on the laboratory scale to large‐area photovoltaic modules requires a significant advance in scalable fabrication methods. Digital inkjet printing promises scalable, material, and cost‐efficient deposition of perovskite thin films on a wide range of substrates and in arbitrary shapes. In this work, high‐quality inkjet‐printed triple‐cation (methylammonium, formamidinium, and cesium) perovskite layers with exceptional thicknesses of >1 µm are demonstrated, enabling unprecedentedly high PCEs > 21% and stabilized power output efficiencies > 18% for inkjet‐printed PSCs. In‐depth characterization shows that the thick inkjet‐printed perovskite thin films deposited using the process developed herein exhibit a columnar crystal structure, free of horizontal grain boundaries, which extend over the entire thickness. A thin film thickness of around 1.5 µm is determined as optimal for PSC for this process. Up to this layer thickness X‐ray photoemission spectroscopy analysis confirms the expected stoichiometric perovskite composition at the surface and shows strong deviations and inhomogeneities for thicker thin films. The micrometer‐thick perovskite thin films exhibit remarkably long charge carrier lifetimes, highlighting their excellent optoelectronic characteristics. They are particularly promising for next‐generation inkjet‐printed perovskite solar cells, photodetectors, and X‐ray detectors.

Section: Resultssupporting

confidence: 90%

Inkjet‐Printed Micrometer‐Thick Perovskite Solar Cells with Large Columnar Grains

Eggers

Schackmar

Abzieher

et al. 2019

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159

167

“…R exp ranging from 0.4 to 1.5 was observed to correlate proportionally to IE, showing that a perovskite film with excess PbI 2 film exhibits a higher IE, while perovskites with excess MAI show smaller IE. This similar trend can also be found by using one‐step solution method and varying the precursor ratios of a lead acetate trihydrate (Pb(Ac) 2 3H 2 O) and MAI . Furthermore, these trends in the energy levels variations are not only characteristic to MAPbI 3 but also to mixed halide perovskites of MAPb(I 1− x Br x ) 3 and MAPb(I 1− x Cl x ) 3 72e.…”

Section: Ensemble Averaged Properties Influencing Solar Cell Parameterssupporting

confidence: 73%

“…XPS is a widely employed surface science technique to investigate the surface chemical composition. A few systematic studies provide insights on the large variations in IE (ranging from 5.1 to 6.6 eV) and EA (3.9 to 4.6 eV) reported in literature 70,72c,e. Meerholz, Olthof, and co‐workers investigated the dependence of chemical composition (XPS) and corresponding energetics (UPS) by preparing 15 solution processed samples and 23 vapor deposited samples with various preparation conditions such as varying precursors molar ratios and annealing parameters 72c.…”

Section: Ensemble Averaged Properties Influencing Solar Cell Parametersmentioning

confidence: 99%

Progress of Surface Science Studies on ABX₃‐Based Metal Halide Perovskite Solar Cells

Qiu

Ono

et al. 2019

103

ABX3 type metal halide perovskite solar cells (PSCs) have shown efficiencies over 25%, rocketing toward their theoretical limit. To gain the full potential of PSCs relies on the understanding of the device working mechanisms and recombination, the material quality, and the match of energy levels in the device stacks. In this review, the importance of designing PSCs from the viewpoint of surface/interface science studies is presented. For this purpose, recent case studies are discussed to demonstrate how probing of local heterogeneities (e.g., grains, grain boundaries, atomic structure, etc.) in perovskites by surface science techniques can help correlate material properties and PSC device performance. At the solar cell device level with active areas larger than millimeter scale, the ensemble average measurement techniques can characterize the overall average properties of perovskite films as well as their adjacent layers and provide clues to understand better the solar cell parameters. How generation and healing of electronic defects in perovskite films limit the device efficiency, reproducibility, and stability, and induce the time‐dependent transient behavior in the current‐voltage curves are also the central focus of this review. On the basis of these studies, strategies to further improve efficiency and stability, as well as reducing hysteresis are presented.

“…Since carriers can accumulate on these low‐bandgap regions, fractions of radiative recombination can be very high, and thus there is a large overall increase in the PL intensity . We note that unintentional fractional deviations in the precursor solution stoichiometry can also impact the extent and sign of photobrightening (or darkening) in perovskite films, a variable which would further contribute to the inconsistencies of reported results . It is reported that the PL intensity increases under continuous illumination in oxygen‐rich conditions even in multication perovskites such as (FA,MA,Cs)PbI 3 , but the extent and rate of this increase is in general lower compared to the MAPbI 3 analogues, suggesting there is at least to some degree a suppression of the photobrightening or photodarkening effects in those compositions .…”

Section: Sensitivity To Sample Morphology Composition and Passivationmentioning

confidence: 85%

Photobrightening in Lead Halide Perovskites: Observations, Mechanisms, and Future Potential

Andaji‐Garmaroudi

Anaya

Pearson

et al. 2019

There has been a meteoric rise in the commercial potential of lead halide perovskite optoelectronic devices since photovoltaic cells and light‐emitting diodes based on these materials were first demonstrated. One key challenge common to each of these optoelectronic devices is the need to suppress nonradiative recombination, a process that limits the maximum achievable efficiency in photovoltaic cells and light‐emitting diodes. In this Progress Report, recent studies that seek to minimize this loss pathway in perovskites through a photobrightening treatment, whereby the luminescence efficiency is enhanced through a light illumination passivation process are examined. The sensitivity of this effect to various experimental considerations is examined, including atmosphere, photon energy, photon dose, and also the role of perovskite composition and morphology; under certain conditions there can even be photodarkening effects. Consideration of these factors is critical to resolve seemingly conflicting literature reports. Proposed mechanisms are scrutinized, revealing that there is now some consensus but further work is needed to identify the specific defects being passivated and elucidate universal mechanisms. Finally, the prospects for these treatments to minimize halide migration and push the properties of polycrystalline films towards those of their single‐crystal counterparts are discussed.