This review article examines the current state of understanding in how metal halide perovskite solar cells can degrade when exposed to moisture, oxygen, heat, light, mechanical stress, and reverse ...bias. It also highlights strategies for improving stability, such as tuning the composition of the perovskite, introducing hydrophobic coatings, replacing metal electrodes with carbon or transparent conducting oxides, and packaging. The article concludes with recommendations on how accelerated testing should be performed to rapidly develop solar cells that are both extraordinarily efficient and stable.
The emergence over the past four years of solar cells made by solution casting thin lms of light-absorbing methylammonium lead halide perovskite semiconductors has captured the attentionof materials ...scientists and researchers in renewable energy13. The 15% efficiency values reported nearly a year ago ignited an explosion of research in this eld (Fig.1). Unsurprisingly, researchers quickly identied challenges that needed to be addressedfor these materials to be technologically successful. Writing in NatureMaterials, NamJoongJeon and colleagues4 now report a deposition approach that, by signicantly improving the morphology control of the perovskite layers, provides a feasible strategy to overcome some of these problems and raises expectations for these semiconductors.
Understanding the degradation mechanisms of organic photovoltaics is particularly important, as they tend to degrade faster than their inorganic counterparts, such as silicon and cadmium telluride. ...An overview is provided here of the main degradation mechanisms that researchers have identified so far that cause extrinsic degradation from oxygen and water, intrinsic degradation in the dark, and photo‐induced burn‐in. In addition, it provides methods for researchers to identify these mechanisms in new materials and device structures to screen them more quickly for promising long‐term performance. These general strategies will likely be helpful in other photovoltaic technologies that suffer from insufficient stability, such as perovskite solar cells. Finally, the most promising lifetime results are highlighted and recommendations to improve long‐term performance are made. To prevent degradation from oxygen and water for sufficiently long time periods, OPVs will likely need to be encapsulated by barrier materials with lower permeation rates of oxygen and water than typical flexible substrate materials. To improve stability at operating temperatures, materials will likely require glass transition temperatures above 100 °C. Methods to prevent photo‐induced burn‐in are least understood, but recent research indicates that using pure materials with dense and ordered film morphologies can reduce the burn‐in effect.
Understanding the degradation mechanisms that reduce the long‐term stability in organic photovoltaics is imperative. The present understanding of degradation mechanisms and the strategies researchers can use to identify them in new materials are reviewed. Some of the relevant materials properties that can be tuned to improve the long‐term performance of organic photovoltaics are identified.
Thinner Si solar cells with higher efficiency can make a Si photovoltaic system a cost-effective energy solution, and nanostructuring has been suggested as a promising method to make thin Si an ...effective absorber. However, thin Si solar cells with nanostructures are not efficient because of severe Auger recombination and increased surface area, normally yielding <50% EQE with short-wavelength light. Here we demonstrate >80% EQEs at wavelengths from 400 to 800 nm in a sub-10-μm-thick Si solar cell, resulting in 13.7% power conversion efficiency. This significant improvement was achieved with an all-back-contact design preventing Auger recombination and with a nanocone structure having less surface area than any other nanostructures for solar cells. The device design principles presented here balance the photonic and electronic effects together and are an important step to realizing highly efficient, thin Si and other types of thin solar cells.
Charge generation in champion organic solar cells is highly efficient in spite of low bulk charge‐carrier mobilities and short geminate‐pair lifetimes. In this work, kinetic Monte Carlo simulations ...are used to understand efficient charge generation in terms of experimentally measured high local charge‐carrier mobilities and energy cascades due to molecular mixing.
Challenges for commercializing perovskite solar cells Rong, Yaoguang; Hu, Yue; Mei, Anyi ...
Science (American Association for the Advancement of Science),
2018-Sep-21, 2018-09-21, 20180921, Volume:
361, Issue:
6408
Journal Article
Peer reviewed
Perovskite solar cells (PSCs) have witnessed rapidly rising power conversion efficiencies, together with advances in stability and upscaling. Despite these advances, their limited stability and need ...to prove upscaling remain crucial hurdles on the path to commercialization. We summarize recent advances toward commercially viable PSCs and discuss challenges that remain. We expound the development of standardized protocols to distinguish intrinsic and extrinsic degradation factors in perovskites. We review accelerated aging tests in both cells and modules and discuss the prediction of lifetimes on the basis of degradation kinetics. Mature photovoltaic solutions, which have demonstrated excellent long-term stability in field applications, offer the perovskite community valuable insights into clearing the hurdles to commercialization.
Tin and lead iodide perovskite semiconductors of the composition AMX3, where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because ...they have band gaps that can be tuned over a wide range by compositional substitution. We experimentally identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX6 octahedra or by simply contracting the lattice isotropically. The former effect tends to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive reduction of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation composition. Using this strategy, we demonstrate solar cells that harvest light in the infrared up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. The mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.
2,2′,7,7′-Tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), the prevalent organic hole transport material used in solid-state dye-sensitized solar cells and ...perovskite-absorber solar cells, relies on an uncontrolled oxidative process to reach appreciable conductivity. This work presents the use of a dicationic salt of spiro-OMeTAD, named spiro(TFSI)2, as a facile means of controllably increasing the conductivity of spiro-OMeTAD up to 10–3 S cm–1 without relying on oxidation in air. Spiro(TFSI)2 enables the first demonstration of solid-state dye-sensitized solar cells fabricated and operated with the complete exclusion of oxygen after deposition of the sensitizer with higher and more reproducible device performance. Perovskite-absorber solar cells fabricated with spiro(TFSI)2 show improved operating stability in an inert atmosphere. Gaining control of the conductivity of the HTM in both dye-sensitized and perovskite-absorber solar cells in an inert atmosphere using spiro(TFSI)2 is an important step toward the commercialization of these technologies.
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