Search

Perovskite solar cells (PSCs) represent one of the most promising emerging photovoltaic technologies due to their high power conversion efficiency. However, despite the huge progress made not only in terms of the efficiency achieved, but also fundamental understanding of the relevant physics of the devices and issues which affect their efficiency and stability, there are still unresolved problems and obstacles on the path toward commercialization of this promising technology. In this roadmap, we aim to provide a concise and up to date summary of outstanding issues and challenges, and the progress made toward addressing these issues. While the format of this article is not meant to be a comprehensive review of the topic, it provides a collection of the viewpoints of the experts in the field, which covers a broad range of topics related to PSC commercialization, including those relevant for manufacturing (scaling up, different types of devices), operation and stability (various factors), and environmental issues (in particular the use of lead). We hope that the article will provide a useful resource for researchers in the field and that it will facilitate discussions and move forward toward addressing the outstanding challenges in this fast-developing field.

Perovskite solar cells (PSCs) represent one of the most promising emerging photovoltaic technologies due to their high power conversion efficiency. However, despite the huge progress made not only in terms of the efficiency achieved, but also fundamental understanding of the relevant physics of the devices and issues which affect their efficiency and stability, there are still unresolved problems and obstacles on the path toward commercialization of this promising technology. In this roadmap, we aim to provide a concise and up to date summary of outstanding issues and challenges, and the progress made toward addressing these issues. While the format of this article is not meant to be a comprehensive review of the topic, it provides a collection of the viewpoints of the experts in the field, which covers a broad range of topics related to PSC commercialization, including those relevant for manufacturing (scaling up, different types of devices), operation and stability (various factors), and environmental issues (in particular the use of lead). We hope that the article will provide a useful resource for researchers in the field and that it will facilitate discussions and move forward toward addressing the outstanding challenges in this fast-developing field.

Various phosphonic acid based self-assembled monolayers (SAMs) have been commonly used for interface modifications in inverted perovskite solar cells. This typically results in significant enhancement of the hole extraction and consequent increase in the power conversion efficiency. However, the surface coverage and packing density of SAM molecules can vary, depending on the chosen SAM material and underlying oxide layer. In addition, different SAM molecules have diverse effects on the interfacial energy level alignment and perovskite film growth, resulting in complex relationships between surface modification, efficiency, and lifetime. Here we show that ethanolamine surface modification combined with [2-(9H-carbazol-9-yl)ethyl]-phosphonic acid (2PACz) results in significant improvement in device stability compared to devices with 2PACz modification only. The significantly smaller size of ethanolamine enables it to fill any gaps in 2PACz coverage and provide improved interfacial defect passivation, while its different chemical structure enables it to provide complementary effects to 2PACz passivation. Consequently, the perovskite films are more stable under illumination (slower photoinduced segregation), and the devices exhibit significant stability enhancement. Despite similar power conversion efficiencies (PCE) between 2PACz only and combined ethanolamine-2PACz modification (PCE of champion devices similar to 21.6-22.0% for rigid and similar to 20.2-21.0% for flexible devices), the T-80 lifetime under simulated solar illumination in ambient is improved more than 15 times for both and flexible devices.

We investigated the influence of two passivating moleculescontaininga P=O group on the performance of quasi-2D Dion-Jacobsonhalide perovskite light-emitting diodes, namely, triphenylphosphineoxide (TPPO) and diphenyl-4-triphenylsilylphenyl phosphine oxide (TSPO1).We found that both passivating molecules lead to increased efficiencycompared to control devices, while they had opposite effects on devicelifetime, with a decrease observed for TPPO and an increase observedfor TSPO1. The two passivating molecules resulted in differences inenergy-level alignment, electron injection, film morphology and crystallinity,and ion migration during operation. While TPPO resulted in mproved photoluminescence decay times, overall higher maximum external quantumefficiency (EQE) and device lifetime were obtained for TSPO1 comparedto TPPO (14.4% vs 12.4% EQE, 341 min vs 42 min T-50).

Tin-based halide perovskite materials are of interest for light-emitting applications due to their broad yellow emission, but they are known to exhibit inferior stability compared to lead-based perovskites due to the tendency of Sn2+ to be readily oxidized. Here, we investigated the ambient stability of a Dion-Jacobson tin bromide perovskite. We found that the optical properties of the samples were more significantly affected by moisture rather than the ratio of Sn2+/Sn4+. The exposure to humidity resulted in changes in the ratio of 2D HDASnBr(4) and hydrated 1D HDA(3)SnBr(8) phases (where HDA denotes hexane-1,6-diammonium), with an initial increase (up to similar to 40 h) in luminescence attributed to the increasing fraction of the hydrated 1D phase which contributes to self-trapped exciton emission. With further exposure to humidity, the material starts to degrade resulting in reduced luminescence after similar to 40 h. The use of additives for the suppression of oxidation of Sn2+, namely SnCl2 and tetraethyl orthosilicate (TEOS), results in prolonging the lifetime of the samples (>260 h for thin films with additives, compared to 180 h for thin films without additives). However, the persistence of luminescence with an increased time of ambient exposure in samples prepared with additives can be attributed to the changes in the evolution of phase compositions (ratios of 2D and hydrated 1D phases) over time rather than suppression of the oxidation of Sn2+.

Perovskite solar cells (PSCs) are known to be sensitive to the exposure to ambient humidity, which typically results in the degradation and deterioration of performance, although positive effects of exposure to moisture have also been reported, due to recrystallization of the perovskite. Common approach to improve stability is to use 3D/2D perovskite active layer, where 2D capping layer is prepared by spin coating the bulky organic cation halide. Herein, it is shown that optimizing the exposure of the capping layer prepared by spin coating phenylethylammonium iodide (PEAI) to ambient atmosphere results in substantial improvement of the PSC performance. Furthermore, the initial effects of PEAI treatment are dependent on the NiOx/perovskite interface, but in all cases except at very high humidity (80–85% RH) optimized exposure to ambient results in improved performance. The variations in device performance with PEAI treatment and ambient exposure can be attributed to defect passivation and changes in the charge extraction due to energy-level alignment at the interfaces. The best performing devices have passivation of NiOx/perovskite interface and PEAI treatment of top surface followed by exposure to ambient atmosphere at RH of 40–45%, which results in the power conversion efficiency increase from 20.3% to 22.4%.

Significant enhancement of the light emission in Ruddlesden–Popper organic–inorganic halide perovskites is obtained by antisolvent induced spontaneous formation of nanocrystals in an amorphous matrix. This morphology change results in the passivation of defects and significant enhancement of light emission and 16 times higher photoluminescence quantum yield (PLQY), and it is applicable to different spacer cations. The use of trioctylphosphine oxide results in further defect passivation leading to an increase in PLQY (≈2.3 times), the suppression of lower energy emission in low temperature photoluminescence spectra, the dominance of radiative recombination, and the disappearance of thermal quenching of the luminescence. The proposed method offers a reproducible, controllable, and antisolvent‐insensitive alternative to energy landscape engineering to utilize energy funneling phenomenon to achieve bright emission. Instead of facilitating fast energy transfer from lower to higher number of perovskite sheets to prevent nonradiative losses, it is demonstrated that defects can be effectively passivated via morphology control and the use of a passivating agent, so that bright emission can be obtained from single phase nanocrystals embedded in amorphous matrix, resulting in light emitting diodes with a maximum external quantum efficiency of 2.25%.

Ruddlesden–Popper halide perovskite (RPP) materials are of significant interest for light-emitting devices since their emission wavelength can be controlled by tuning the number of layers n, resulting in improved spectral stability compared to mixed halide devices. However, RPP films typically contain phases with different n, and the low n phases tend to be unstable upon exposure to humidity, irradiation, and/or elevated temperature which hinders the achievement of pure blue emission from n = 2 films. In this work, two spacer cations are used to form an RPP film with mixed cation bilayer and high n = 2 phase purity, improved stability, and brighter light emission compared to a single spacer cation RPP. The stabilization of n = 2 phase is attributed to favorable formation energy, reduced strain, and reduced electron–phonon coupling compared to the RPP films with only one type of spacer cation. Using this approach, pure blue light-emitting diodes (LEDs) with Commission Internationale de l'éclairage (CIE) coordinates of (0.156, 0.088) and excellent spectral stability are achieved. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Imaging of biological matter by using fluorescent nanoparticles (NPs) is becoming a widespread method for in vitro imaging. However, currently there is no fluorescent NP that satisfies all necessary criteria for short-term in vivo imaging: biocompatibility, biodegradability, photostability, suitable wavelengths of absorbance and fluorescence that differ from tissue auto-fluorescence, and near infrared (NIR) emission. In this paper, we report on the photoluminescent properties of magnesium oxide (MgO) NPs that meet all these criteria. The optical defects, attributed to vanadium and chromium ion substitutional defects, emitting in the NIR, are observed at room temperature in NPs of commercial and in-house ball-milled MgO nanoparticles, respectively. As such, the NPs have been successfully integrated into cultured cells and photostable bright in vitro emission from NPs was recorded and analyzed. We expect that numerous biotechnological and medical applications will emerge as this nanomaterial satisfies all criteria for short-term in vivo imaging.