A User Study on Explainable Online Reinforcement Learning for Adaptive Systems

Online reinforcement learning (RL) is increasingly used for realizing adaptive systems in the presence of design time uncertainty. Online RL facilitates learning from actual operational data and thereby leverages feedback only available at runtime. However, Online RL requires the definition of an effective and correct reward function, which quantifies the feedback to the RL algorithm and thereby guides learning. With Deep RL gaining interest, the learned knowledge is no longer explicitly represented, but is represented as a neural network. For a human, it becomes practically impossible to relate the parametrization of the neural network to concrete RL decisions. Deep RL thus essentially appears as a black box, which severely limits the debugging of adaptive systems. We previously introduced the explainable RL technique XRL-DINE, which provides visual insights into why certain decisions were made at important time points. Here, we introduce an empirical user study involving 54 software engineers from academia and industry to assess (1) the performance of software engineers when performing different tasks using XRL-DINE and (2) the perceived usefulness and ease of use of XRL-DINE.Comment: arXiv admin note: substantial text overlap with arXiv:2210.0593

Smartphone‐Based Luminescent Thermometry via Temperature‐Sensitive Delayed Fluorescence from Gd0_{0}O2_{2}S:Eu3+^{3+}

Thermal images generated from infrared radiation are useful for monitoring many processes; however, infrared cameras are orders of magnitude more expensive than their visible counterparts. Methods that allow visible cameras to capture thermal images are therefore of interest. In this contribution, thermal images of a surface coated with an inexpensive inorganic micropowder phosphor are generated from the analysis of a video taken with a smartphone camera. The phosphor is designed to have a temperature‐dependent emission lifetime that is long enough to be determined from the analysis of a 30 frames‐per‐second video recording. This proof‐of‐principle work allows temperatures in the 270–320 K range to be accurately determined with a precision better than 2 K, even in the presence of bright background illuminance up to 1500 lm m$^{-2}$. In the broader context, this inspires further development of phosphors to bring time‐resolved sensing techniques into lifetime long enough ranges to allow smartphone‐based detection

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

In Situ Process Monitoring and Multichannel Imaging for Vacuum‐Assisted Growth Control of Inkjet‐Printed and Blade‐Coated Perovskite Thin‐Films

Vacuum-assisted growth (VAG) control is one of the most promising methods for controlling nucleation and crystallization of printed and coated large area lead halide perovskite-based layers for optoelectronics. To coat or print homogeneous high-quality perovskite thin-films at high fabrication yield, real-time process monitoring of the VAG is pivotal. In response, a 2.1-megapixel multichannel photoluminescence (PL) and reflection imaging system is developed and employed for the simultaneous spatial in situ analysis of drying, nucleation, and crystal growth during VAG and subsequent thermal annealing of inkjet-printed and blade-coated perovskite thin-films. It is shown that the VAG process, for example, evacuation rate and time, affects the film formation and provide detailed insight into traced PL and reflection transients extracted from sub-second videos of each channel. Based on correlative analysis between the transients and, for example, perovskite ink composition, wet-film thickness, or evacuation time, key regions which influence crystal quality, film morphology, and are base for prediction of solar cell performance are identified

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

Laminated Monolithic Perovskite/Silicon Tandem Photovoltaics

Perovskite/silicon tandem photovoltaics have attracted enormous attention in science and technology over recent years. In order to improve the performance and stability of the technology, new materials and processes need to be investigated. However, the established sequential layer deposition methods severely limit the choice of materials and accessible device architectures. In response, a novel lamination process that increases the degree of freedom in processing the top perovskite solar cell (PSC) is proposed. The very first prototypes of laminated monolithic perovskite/silicon tandem solar cells with stable power output efficiencies of up to 20.0% are presented. Moreover, laminated single-junction PSCs are on par with standard sequential layer deposition processed devices in the same architecture. The numerous advantages of the lamination process are highlighted, in particular the opportunities to engineer the perovskite morphology, which leads to a reduction of non-radiative recombination losses and and an enhancement in open-circuit voltage (Voc). Laminated PSCs exhibit improved stability by retaining their initial efficiency after 1-year aging and show good thermal stability under prolonged illumination at 80 °C. This lamination approach enables the research of new architectures for perovskite-based photovoltaics and paves a new route for processing monolithic tandem solar cells even with a scalable lamination process

Triple-junction perovskite-perovskite-silicon solar cells with power conversion efficiency of 24.4%

The recent tremendous progress in monolithic perovskite-based double-junction solar cells is just the start of a new era of ultra-high-efficiency multi-junction photovoltaics. We report on triple-junction perovskite-perovskite-silicon solar cells with a record power conversion efficiency of 24.4%. Optimizing the light management of each perovskite sub-cell (∼1.84 and ∼1.52 eV for top and middle cells, respectively), we maximize the current generation up to 11.6 mA cm−2. Key to this achievement was our development of a high-performance middle perovskite sub-cell, employing a stable pure-α-phase high-quality formamidinium lead iodide perovskite thin film (free of wrinkles, cracks, and pinholes). This enables a high open-circuit voltage of 2.84 V in a triple junction. Non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency if stored in the dark at 85 °C for 1081 h

Scalable two-terminal all-perovskite tandem solar modules with a 19.1% efficiency

Monolithic all-perovskite tandem photovoltaics promise to combine low-cost and high-efficiency solar energy harvesting with the advantages of all-thin-film technologies. To date, laboratory-scale all-perovskite tandem solar cells have only been fabricated using non-scalable fabrication techniques. In response, this work reports on laser-scribed all-perovskite tandem modules processed exclusively with scalable fabrication methods (blade coating and vacuum deposition), demonstrating power conversion efficiencies up to 19.1% (aperture area, 12.25 cm2; geometric fill factor, 94.7%) and stable power output. Compared to the performance of our spin-coated reference tandem solar cells (efficiency, 23.5%; area, 0.1 cm2), our prototypes demonstrate substantial advances in the technological readiness of all-perovskite tandem photovoltaics. By means of electroluminescence imaging and laser-beam-induced current mapping, we demonstrate the homogeneous current collection in both subcells over the entire module area, which explains low losses (<5%rel) in open-circuit voltage and fill factor for our scalable modules