Showing papers by "Jan D'Haen published in 2022"

Critical Role of Perovskite Film Stoichiometry in Determining Solar Cell Operational Stability: a Study on the Effects of Volatile A-Cation Additives.

Abstract: Volatile A-cation halide (AX) additives such as formamidinium chloride and methylammonium chloride have been widely employed for high-efficiency perovskite solar cells (PSCs). However, it remains unstudied how they influence the perovskite film stoichiometry and the solar cell performance and operational stability. Hereby, our work shows that over annealing of formamidinium chloride-containing perovskite films leads to a Pb-rich surface, resulting in a high initial efficiency, which however decays during maximum power point tracking (MPPT). On the contrary, perovskite films obtained by a shorter annealing time at the same temperature provide good stability during MPPT but a lower initial efficiency. Thus, we deduce that an optimal annealing is vital for both high efficiency and operational stability, which is then confirmed in the case where methylammonium chloride additive is used. With optimized perovskite annealing conditions, we demonstrate efficient and stable p-i-n PSCs that show a best power conversion efficiency of 20.7% and remain 90% of the initial performance after a 200 h MPPT at 60 °C under simulated 1 sun illumination with high UV content. Our work presents a comprehensive understanding on how volatile AX impacts perovskite film stoichiometry and its correlation to the device performance and operational stability, providing a new guideline for fabricating high-efficiency and operationally stable PSCs.

Temperature-Driven Chemical Segregation in Co-Free Li-Rich-Layered Oxides and Its Influence on Electrochemical Performance

Abstract: Co-free Li-rich layered oxides are gaining interest as feasible positive electrode materials in lithium-ion batteries (LIBs) in terms of energy density, cost reduction, and alleviating safety concerns. Unfortunately, their commercialization is hindered by severe structural degradation that occurs during electrochemical operation. The study at hand demonstrates advanced structural engineering of a Li-rich Co-free oxide with composition Li1.1Ni0.35Mn0.55O2 by spray pyrolysis and subsequent calcination of an aqueous precursor, creating a segregated structure of two distinct layered phases with space groups R3̅m (rhombohedral) and C2/m (monoclinic). This particular structure was investigated with powder neutron diffraction, high-resolution analytical transmission electron microscopy imaging, and electron energy loss spectroscopic characterization. This complex structure contributes to the high electrochemical stability and good rate capability observed for this compound (160 mAh/g at C/3 and 100 mAh/g at 1C). These results provide new insights into the feasibility of developing and commercializing cobalt-free positive electrode materials for LIBs.

A study of quenching approaches to optimize ultrasonic spray coated perovskite layers scalable for PV

Abstract: Perovskite materials have gathered increased interest over the last decade. Their rapidly rising efficiency, coupled with the compatibility with solution processing and thin film technology has put perovskite solar cells (PSC) on the spotlight of photovoltaic research. On top of that, band gap tunability via composition changes makes them a perfect candidate for tandem applications, allowing for further harvest of the solar irradiation spectrum and improved power conversion efficiency (PCE). In order to convert all these advantages into large scale production and have increased dissemination in the energy generation market, perovskite fabrication must be adapted and optimized with the use of high throughput, continuous processes, such as ultrasonic spray coating (USSC). In this paper we investigate the ultrasonically spray coated perovskite layers for photovoltaic applications, with particular focus on the quenching-assisted crystallization step. Different quenching techniques are introduced to the process and compared in terms of final layer morphology and cell performance. Finally, gas quenching is used with the large-scale-compatible deposition and allows the production of perovskite solar cells with PCE >15%.

Interrelationships among adjustable design parameters and rate performance of porous electrodes in lithium‐ion batteries

Abstract: A combination of experiments and physics-based modeling is used to highlight the complex interaction among the adjustable design parameters of porous electrodes in determining the capacity and rate performance of lithium-ion batteries (LIBs). A series of 52 LiMn2O4 electrodes are prepared with loading and porosity in the range of 10 to 30 mg cm−2 and 0.2 to 0.5, respectively, and cycled at different C-rates in front of Li. A detailed polarization analysis of the 96 discharge profiles points to the absence of any ubiquitous sharp and universal correlation between the lumped macroscopic indexes such as the electrode thickness and the battery performance. The results call for a careful attention to the nonlinear response of the LIBs to the design variations and the significance of big data analysis to reveal the peculiar interrelationships between the battery performance and the detailed features of the electrodes such as the configuration and spatial distribution of the (in)active particles.