Managing Interfacial Charged Defects with Multiple Active Sited Macrocyclic Valinomycin for Efficient and Stable Inverted Perovskite Solar Cells

Anion Binding Interaction Enhances the Robustness of Iodide for High-Performance Perovskite Solar Cells

Owing to the ionic bond nature of the Pb-I bond, the iodide at the interface of perovskite polycrystalline films was easily lost during the preparation process, resulting in the formation of a large number of iodine vacancy defects. The presence of iodine vacancy defects can cause nonradiative recombination, provide a pathway for iodide migration, and be harmful to the power conversion efficiency (PCE) and stability of organic-inorganic hybrid perovskite solar cells (HPSCs). Here, in order to increase the robustness of iodides at the interface, a strategy to introduce anion binding effects was developed to stabilize the perovskite films. It was demonstrated that the N,N'-diphenylurea (DPU), characterized by high anionic binding constants and a Y-shaped structure, provides a relatively strong hydrogen bond donor site to effectively reduce the iodine loss during film preparation and inhibits iodide migration in the device working condition. As expected, the reduced iodine loss considerably improves the quality of the perovskite films and suppresses nonradiative recombination. The performance of the device after DPU modification was significantly increased, with the PCE rising from 23.65 to 25.01% with huge stability enhancement as well.

Multifunctional Biomolecules Bridging a Buried Interface for Efficient Perovskite Solar Cells

The inevitably positively and negatively charged defects on the SnO2/perovskite buried interface often lead to nonradiative recombination of carriers and unfavorable alignment of energy levels in perovskite solar cells (PSCs). Interface engineering is a reliable strategy to manage charged defects. Herein, the nicotinamide adenine dinucleotide (NAD) molecules with multiple active groups of ─P=O, ─P-O, and ─NH2 are introduced to bridge the SnO2/perovskite buried interface for achieving simultaneous elimination of positively and negatively charged defects. We demonstrate that the ─P=O and ─P-O groups in NAD not only fix the uncoordinated Pb2+ but also fill the oxygen vacancies (VO) on the SnO2 layer to eliminate positively charged defects. Meanwhile, ─NH2 groups form hydrogen bonds with PbI2 to reduce the number of negatively charged defects. In addition, the NAD biomolecules as a bridge induce high perovskite crystallization and accelerated electronic transfer along with favorable energy band alignment between SnO2 and perovskite. Finally, the PSCs with the ITO/SnO2/NAD/Cs0.15FA0.75MA0.1PbI3/Spiro-OMeTAD/Ag structure deliver an improvement in the power conversion efficiency from 20.49 to 23.18% with an excellent open-circuit voltage (Voc) of 1.175 V. This work demonstrates that interface engineering through multifunctional molecular bridges with various functional groups is an effective approach to improve the performance of PSCs by eliminating charged defects and simultaneously regulating energy level alignment.

Efficient Charge Transport in Inverted Perovskite Solar Cells via 2D/3D Ferroelectric Heterojunction

While the 2D/3D heterojunction is an effective method to improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs), carriers are often confined in the quantum wells (QWs) due to the unique structure of 2D perovskite, which makes the charge transport along the out-of-plane direction difficult. Here, a 2D/3D ferroelectric heterojunction formed by 4,4-difluoropiperidine hydrochloride (2FPD) in inverted PSCs is reported. The enriched 2D perovskite (2FPD)2PbI4 layer with n = 1 on the perovskite surface exhibits ferroelectric response and has oriented dipoles along the out-of-plane direction. The ferroelectricity of the oriented dipole layer facilitates the enhancement of the built-in electric field (1.06 V) and the delay of the cooling process of hot carriers, reflected in the high carrier temperature (above 1400 K) and the prolonged photobleach recovery time (139.85 fs, measured at bandgap), improving the out-of-plane conductivity. In addition, the alignment of energy levels is optimized and exciton binding energy (32.8 meV) is reduced by changing the dielectric environment of the surface. Finally, the 2FPD-treated PSCs achieve a PCE of 24.82% (certified: 24.38%) with the synergistic effect of ferroelectricity and defect passivation, while maintaining over 90% of their initial efficiency after 1000 h of maximum power point tracking.

Novel Strategy for High Efficient and Stable Perovskite Solar Cells through Atomic Layer Deposition

The perovskite material has demonstrated conceivable potential as an absorbing material of solar cells. Although the power conversion efficiency of the device based on perovskite has rapidly come to 26%, there are still many factors that affect the further improvement of the photoelectric conversion efficiency. Interface defects are the dominating concern that influence carrier transportation and stability. Here, we report a novel strategy where B2O3 is deposited on the fresh perovskite film by atomic layer deposition technology. The organic atmosphere during atomic layer deposition can effectively regulate the crystallization kinetics of perovskites and promote crystal growth. The B2O3 adsorbed on the perovskite light-absorption layer can effectively reduce the electropositive defects on the surface of the perovskite, such as uncoordinated Pb2+ and I vacancies due to the electron-donating properties of the side O atoms in B2O3. Consequently, the power conversion efficiency of the perovskite solar cell after B2O3 treatment increases to 21.78% from 18.89%. Simultaneously, B2O3 can improve the stability of devices.

Modulation of Buried Interface by 1-(3-aminopropyl)-Imidazole for Efficient Inverted Formamidinium-Cesium Perovskite Solar Cells

Considering the direct influence of substrate surface nature on perovskite (PVK) film growth, buried interfacial engineering is crucial to obtain ideal perovskite solar cells (PSCs). Herein, 1-(3-aminopropyl)-imidazole (API) is introduced at polytriarylamine (PTAA)/PVK interface to modulate the bottom property of PVK. First, the introduction of API improves the growth of PVK grains and reduces the Pb2+ defects and residual PbI2 present at the bottom of the film, contributing to the acquisition of high-quality PVK film. Besides, the presence of API can optimize the energy structure between PVK and PTAA, which facilitates the interfacial charge transfer. Density functional theory (DFT) reveals that the electron donor unit (R-C ═ N) of the API prefers to bind with Pb2+ traps at the PVK interface, while the formation of hydrogen bonds between the R-NH2 of API and I- strengthens the above binding ability. Consequently, the optimum API-treated inverted formamidinium-cesium (FA/Cs) PSCs yields a champion power conversion efficiency (PCE) of 22.02% and exhibited favorable stability.

Synergistic Defect Passivation and Crystallization Modulation in Efficient Perovskite Solar Cells: The Case of Multifunctional 2-Anisidine-4-Sulfonic Acid

With the continuous development of the performance of perovskite solar cells, the high-density defects on the perovskite film surface and grain boundaries as well as undesired perovskite crystallization are increasingly emerging as challenges to their commercial application. Herein, a dye intermediate 2-anisidine-4-sulfonic acid (2A4SA), containing sulfonic acid group (SO3-), amino group (-NH2), methoxy group (CH3O-), and benzene ring, which exhibit a synergistic effect in comprehensive defect passivation and crystallization modulation, is incorporated. Detailed investigations show that the SO3- of 2A4SA with high electronegativity firmly chelates with uncoordinated lead ions through the coordination interaction, while the -NH2 and the CH3O- of 2A4SA separately immobilize iodide ions and organic cations in the perovskite lattice through hydrogen bonds, enabling substantially decreased nonradiative recombination and trap state density. Meanwhile, 2A4SA molecules attached to the surface of perovskite nuclei can delay crystallization kinetics and promote preferred vertical growth orientation, thereby attaining the high-crystallinity and large-size-grain perovskite films. Consequently, the 2A4SA-doped device with the structure ITO/SnO2/Cs0.15FA0.75MA0.10PbI3 (2A4SA)/Spiro-OMeTAD/Ag presents a splendid power conversion efficiency (PCE) of 23.06% accompanied by increased open-circuit voltage (1.15 V) and fill factor (82.17%). Furthermore, the optimized film and device demonstrate enhanced long-term stability. The unencapsulated optimized device retains ≈80% of the original PCE after 1000 h upon exposure to ambient atmosphere (20-50% RH), whereas the control group is only 56.8%.