In Situ Characterization and Modelling of Drying Dynamics for Scalable Printing of Hybrid Perovskite Photovoltaics

Hybrid perovskite photovoltaics could play a vital role in future’s renewable energy production. However, there are still severe challenges when scaling the technology. In this work, perovskite solution films drying in laminar and slot-jet air flows are investigated extensively by optical in situ characterization. The main results are a quantitative model of perovskite drying dynamics and a novel in situ imaging technique – yielding valuable predictions for large-scale perovskite fabrication

Controlling Thin Film Morphology Formation during Gas Quenching of Slot-Die Coated Perovskite Solar Modules

Transferring record power conversion efficiency (PCE) >25 % of spin-coated perovskite solar cells (PSCs) from the laboratory scale to large-area photovoltaic modules requires significant advance in scalable fabrication techniques. In this work, we demonstrate the fundamental interrelation between drying dynamics of slot-die coated precursor solution thin films and the quality of slot-die coated gas quenched polycrystalline perovskite thin films. Well defined drying conditions are established using a temperature-stabilized, movable table and a flow-controlled, oblique impinging slot nozzle purged with nitrogen. The accurately deposited solution thin film on the substrate is recorded by a tilted CCD camera, allowing for in situ monitoring of the perovskite thin film formation. With the tracking of crystallization dynamics during the drying process, we identify critical process parameters needed for the design of optimal drying and gas quenching systems. In addition, defining different drying regimes, we derive practical slot jet adjustments preventing gas backflow and demonstrate large-area, homogeneous and pinhole-free slot-die coated perovskite thin films that result in solar cells with PCEs of up to 18.6 %. Our study reveals key interrelations of process parameters, e.g. the gas flow and drying velocity, and the exact crystallization position with the morphology formation of fabricated thin films, resulting in a homogeneous performance of corresponding solar 50x50 mm2 mini-modules (17.2 %) with only minimal upscaling loss. In addition, we validate a previously developed model on the drying dynamics of perovskite thin films on small-area for slot-die coated areas of ≥100 cm2. The study provides methodical guidelines for the design of future slot-die coating setups and establishes a step forward to a successful transfer of industrial-scale deposition systems beyond brute force optimization

Correlative In Situ Multichannel Imaging for Large-Area Monitoring of Morphology Formation in Solution-Processed Perovskite Layers

To scale up production of perovskite photovoltaics, state-of-the-art laboratory recipes and processes must be transferred to large-area coating and drying systems. The development of in situ monitoring methods that provide real-time feedback for process control is pivotal to overcome this challenge. Herein, correlative in situ multichannel imaging (IMI) obtaining reflectance, photoluminescence intensity, and central photoluminescence emission wavelength images on areas larger than 100 cm2 with subsecond temporal resolution using a simple, cost-effective setup is demonstrated. Installed on top of a drying channel with controllable laminar air flow and substrate temperature, IMI is shown to consistently monitor solution film drying, perovskite nucleation, and perovskite crystallization. If the processing parameters differ, IMI reveals characteristic changes in large-area perovskite formation dynamics already before the final annealing step. Moreover, when IMI is used to study >130 blade-coated devices processed at the same parameters, about 90% of low-performing devices contain coating inhomogeneities detected by IMI. The results demonstrate that IMI should be of value for real-time 2D monitoring and feedback control in industrial-scale, high-throughput fabrication such as roll-to-roll printing

Upscaling of perovskite solar modules: The synergy of fully evaporated layer fabrication and all‐laser‐scribed interconnections

Given the outstanding progress in research over the past decade, perovskite photovoltaics (PV) is about to step up from laboratory prototypes to commercial products. For this to happen, realizing scalable processes to allow the technology to transition from solar cells to modules is pivotal. This work presents all-evaporated perovskite PV modules with all thin films coated by established vacuum deposition processes. A common 532-nm nanosecond laser source is employed to realize all three interconnection lines of the solar modules. The resulting module interconnections exhibit low series resistance and a small total lateral extension down to 160 μm. In comparison with interconnection fabrication approaches utilizing multiple scribing tools, the process complexity is reduced while the obtained geometrical fill factor of 96% is comparable with established inorganic thin-film PV technologies. The all-evaporated perovskite minimodules demonstrate power conversion efficiencies of 18.0% and 16.6% on aperture areas of 4 and 51 cm$^{2}$, respectively. Most importantly, the all-evaporated minimodules exhibit only minimal upscaling losses as low as 3.1%$_{rei}$ per decade of upscaled area, at the same time being the most efficient perovskite PV minimodules based on an all-evaporated layer stack sequence

Intensity Dependent Photoluminescence Imaging for In‐Line Quality Control of Perovskite Thin Film Processing

Large area fabrication of high-quality polycrystalline perovskite thin filmsremains one of the key challenges for the commercial readiness of perovskitephotovoltaic (PV). To enable high-throughput and high-yield processing,reliable and fast in-line characterization methods are required. The presentwork reports on a non-invasive characterization technique based onintensity-dependent photoluminescence (PL) imaging. The change in PLintensity as a function of excitation power density can be approximated by apower-law with exponent k, which is a useful quality indicator for theperovskite layer, providing information about the relative magnitudes ofradiative and non-radiative recombination. By evaluating k-parameter mapsinstead of more established PL intensity images, 2D information is obtainedthat is robust to optically induced artifacts such as intensity variations inexcitation and reflection. Application to various half stacks of a perovskitesolar cell showcase its ability to determine the importance of the interfacebetween the charge transporting and perovskite layers. In addition, thek-parameter correlates to the bulk passivation concentration, enabling rapidassessment of open-circuit voltage variations in the range of 20 mV.Considering expected improvements in data acquisition speed, the presentedk-imaging method will possibly be obtained in real-time, providing large-areaquality control in industrial-scale perovskite PV production

Drying Dynamics of Solution‐Processed Perovskite Thin‐Film Photovoltaics: In Situ Characterization, Modeling, and Process Control

A key challenge for the commercialization of perovskite photovoltaics is the transfer of high‐quality spin coated perovskite thin‐films toward applying industry‐scale thin‐film deposition techniques, such as slot‐die coating, spray coating, screen printing, or inkjet printing. Due to the complexity of the formation of polycrystalline perovskite thin‐films from the precursor solution, efficient strategies for process transfer require advancing the understanding of the involved dynamic processes. This work investigates the fundamental interrelation between the drying dynamics of the precursor solution thin‐film and the quality of the blade coated polycrystalline perovskite thin‐films. Precisely defined drying conditions are established using a temperature‐stabilized drying channel purged with a laminar flow of dry air. The dedicated channel is equipped with laser reflectometry at multiple probing positions, allowing for in situ monitoring of the perovskite solution thin‐film thickness during the drying process. Based on the drying dynamics as measured at varying drying parameters, namely at varying temperature and laminar air flow velocity, a quantitative model on the drying of perovskite thin‐films is derived. This model enables process transfer to industry‐scale deposition systems beyond brute force optimization. Via this approach, homogeneous and pinhole‐free blade coated perovskite thin‐films are fabricated, demonstrating high power conversion efficiencies of up to 19.5% (17.3% stabilized) in perovskite solar cells

Removal of steroid estrogens in carbonaceous and nitrifying activated sludge processes

This is the post-print version of the final paper published in Chemosphere. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.A carbonaceous (heterotrophic) activated sludge process (ASP), nitrifying ASP and a nitrifying/denitrifying ASP have been studied to examine the role of process type in steroid estrogen removal. Biodegradation efficiencies for total steroid estrogens (ΣEST) of 80 and 91% were recorded for the nitrifying/denitrifying ASP and nitrifying ASP respectively. Total estrogen biodegradation (ΣEST) was only 51% at the carbonaceous ASP, however, the extent of biodegradation in the absence of nitrification clearly indicates the important role of heterotrophs in steroid estrogen removal. The low removal efficiency did not correlate with biomass activity for which the ASPcarbonaceous recorded 80 μg kg−1 biomass d−1 compared to 61 and 15 μg kg−1 biomass d−1 at the ASPnitrifying and ASPnitrifying/denitrifying respectively. This finding was explained by a moderate correlation (r2 = 0.55) between total estrogen loading (ΣEST mg m−3 d−1) and biomass activity (μg ΣEST degraded kg−1 d−1) and has established the impact of loading on steroid estrogen removal at full-scale. At higher solids retention time (SRT), steroid estrogen biodegradation of >80% was observed, as has previously been reported. It is postulated that hydraulic retention time (HRT) is as important as SRT as this governs both reaction time and loading. This observation is based on the high specific estrogen activity determined at the ASPcarbonaceous plant, the significance of estrogen loading and the positive linear correlation between SRT and HRT.Public Utilities Board of Singapore, Anglian Water Ltd., Severn Trent Water Ltd., Thames Water Utilities Ltd., United Utilities Plc., and Yorkshire Water Services Ltd

Optimization of SnO2_{2} electron transport layer for efficient planar perovskite solar cells with very low hysteresis†

Nanostructured tin oxide (SnO$_{2}$) is a very promising electron transport layer (ETL) for perovskite solar cells (PSCs) that allows low-temperature processing in the planar n–i–p architecture. However, minimizing current–voltage (J–V) hysteresis and optimizing charge extraction for PSCs in this architecture remains a challenge. In response to this, we study and optimize different types of single- and bilayer SnO$_{2}$ ETLs. Detailed characterization of the optoelectronic properties reveals that a bilayer ETL composed of lithium (Li)-doped compact SnO$_{2}$ (c(Li)-SnO$_{2}$) at the bottom and potassium-capped SnO$_{2}$ nanoparticle layers (NP-SnO$_{2}$) at the top enhances the electron extraction and charge transport properties of PSCs and reduces the degree of ion migration. This results in an improved PCE and a strongly reduced J–V hysteresis for PSCs with a bilayer c(Li)-NP-SnO$_{2}$ ETL as compared to reference PSCs with a single-layer or undoped bilayer ETL. The champion PSC with c(Li)-NP-SnO$_{2}$ ETL shows a high stabilized PCE of up to 18.5% compared to 15.7%, 12.5% and 16.3% for PSCs with c-SnO$_{2}$, c(Li)-SnO$_{2}$ and c-NP-SnO$_{2}$ as ETL, respectively

Rejection of trace organic chemicals by a nanofiltration membrane: the role of molecular properties and effects of caustic cleaning

This study aims to provide further insights to the rejection mechanisms of trace organic chemicals (TrOCs) by nanofiltration (NF). The separation mechanisms of TrOCs by an NF membrane were elucidated by assessing the role of molecular properties and the impact of caustic cleaning on their rejection. All charged TrOCs were rejected by the NF270 membrane by more than 80%. However, the rejection of positively charged TrOCs was lower than that of negatively charged TrOCs with similar molecular sizes and was similar to the rejection of neutral TrOCs. The results suggest that size exclusion, rather than electrostatic repulsion, was a major factor attributing to the rejection of these positively charged TrOCs. The results also showed that the minimum projection area was a better surrogate parameter for molecular dimensions than molecular weight. Our study highlights the need to monitor the rejection of neutral and positively charged TrOCs (particularly those that are normally moderately rejected by the membrane) following caustic cleaning