Inhibition of ion diffusion/migration in perovskite p-n homojunction by polyetheramine insert layer to enhance stability of perovskite solar cells with p-n homojunction structure.

Perovskite p-n homojunctions (PHJ) have been confirmed to play a crucial role in facilitating carrier separation/extraction in the perovskite absorption layer and provide an additional built-in potential, which benefits the inhibition of carrier recombination in perovskite solar cells (PSCs) and ultimately improves device performance. However, the diffusion and migration of ions between n-type and p-type perovskite films, particularly under operational and heating conditions, lead to the degradation of PHJ structures and limit the long-term stability of PSCs with PHJ structure (denoted as PHJ-PSCs). In this study, we propose an insert layer strategy by directly introducing an ultra-thin polyetheramine (PEA) layer between the n-type and p-type perovskite films to address those challenges arising from ion movements. Femtosecond transient absorption (fs-TAS) and photoluminescence (PL) measurements demonstrate that the PHJ (without and with the insert layer) enhances carrier separation/extraction compared to the single n-type perovskite film. Monitoring the evolution of bromine element distribution reveals that the insert layer can efficiently suppress ion diffusion between perovskite films, even under long-term illumination and heating conditions. Consequently, an efficiency of 23.53% with excellent long-term operational stability is achieved in the optimized PHJ-PSC with the insert layer.

Quantitative analysis of molecular transport in the extracellular space using physics-informed neural network.

The brain extracellular space (ECS), an irregular, extremely tortuous nanoscale space located between cells or between cells and blood vessels, is crucial for nerve cell survival. It plays a pivotal role in high-level brain functions such as memory, emotion, and sensation. However, the specific form of molecular transport within the ECS remain elusive. To address this challenge, this paper proposes a novel approach to quantitatively analyze the molecular transport within the ECS by solving an inverse problem derived from the advection-diffusion equation (ADE) using a physics-informed neural network (PINN). PINN provides a streamlined solution to the ADE without the need for intricate mathematical formulations or grid settings. Additionally, the optimization of PINN facilitates the automatic computation of the diffusion coefficient governing long-term molecule transport and the velocity of molecules driven by advection. Consequently, the proposed method allows for the quantitative analysis and identification of the specific pattern of molecular transport within the ECS through the calculation of the Péclet number. Experimental validation on two datasets of magnetic resonance images (MRIs) captured at different time points showcases the effectiveness of the proposed method. Notably, our simulations reveal identical molecular transport patterns between datasets representing rats with tracer injected into the same brain region. These findings highlight the potential of PINN as a promising tool for comprehensively exploring molecular transport within the ECS.

Stable perovskite solar cells with 22% efficiency enabled by inhibiting migration/loss of iodide ions.

Iodide ions (I- and I3-) in perovskites tend to migrate resulting in phase segregation and degradation of perovskite films and devices under illumination or operation conditions. In order to overcome this intrinsic difficulty, passivation and additive strategies have been developed in many studies. In this work, we introduced polyetheramine (PEA) into perovskite films to inhibit the migration and loss of iodides and suppress defects related to these migrated ions. The perovskite films with PEA barely suffered iodide loss even under long-term ultraviolet (UV) illumination and possessed a lower trap density than that of the pristine films before and after aging under UV illumination. Density functional theory (DFT) calculations revealed that PEA can form strong interactions with iodides and Pb2+ in perovskites via PbO and H-I bonds, and the iodide ions (I- and I3-) could be locked firmly by PEA, preventing them from migration or loss. Using this method, the efficiency of perovskite solar cells (PSCs) can be improved from 19.71% (without PEA) to 22.02% (with PEA). After 200 h of maximum power point (MPP) tracking, the efficiency of PSCs with PEA remained 89% of its initial value and that of PSCs without PEA fully degraded.

Inhibition of PbI2-induced defects by doping MABr for high-performance perovskite solar cells.

The performance of FAPbI3-based perovskite solar cells (PSCs) has been drastically improved with a photoelectric conversion efficiency (PCE) of 25.7%, showing attractive application potential. To achieve higher efficiency and longer-term stability of PSCs, a large number of passivation methods are used to inhibit Pb and I defects of FAPbI3 films. In this study, we developed a facile method to suppress the residual PbI2 of perovskite films and the related defects efficiently by a two-step spin-coating process, which prominently improves the carrier lifetime of α-FAPbI3 films (from 459 ns to 1346 ns). In addition, the morphology and crystallization characteristics of the films were also significantly improved, and the grains grew up to 1 µm. The efficiency of FAPbI3-based PSCs fabricated by this method reached 22.64%.