Interfacial Modification via a 1,4-Butanediamine-Based 2D Capping Layer for Perovskite Solar Cells with Enhanced Stability and Efficiency

Eliminating Voids and Residual PbI2 beneath a Perovskite Film via Buried Interface Modification for Efficient Solar Cells

The commercialization process of perovskite solar cells (PSCs) is markedly restricted by the power conversion efficiency (PCE) and long-term stability. During fabrication and operation, the bottom interface of the organic-inorganic hybrid perovskite layer frequently exhibits voids and residual PbI2, while these defects inevitably act as recombination centers and degradation sites, affecting the efficiency and stability of the devices. Therefore, the degradation and nonradiative recombination originating from the buried interface should be thoroughly resolved. Here, we report a multifunctional passivator by introducing malonic dihydrazide as an interfacial chemical bridge between the electron transport layer and the perovskite (PVK) layer. MADH with hydrazine groups improves the surface affinity of SnO2 and provides nucleation sites for the growth of PVK, leading to the reduced residual PbI2 and the voids resulting from the inhomogeneous solvent volatilization at the bottom interface. Meanwhile, the hydrazine group and carbonyl group synergistically coordinate with Pb2+ to improve the crystal growth environment, reducing the number of Pb-related defects. Eventually, the PCE of the PSCs is significantly enhanced benefiting from the reduced interfacial defects and the increased carrier transport. Moreover, the reductive nature of hydrazide further inhibits I2 generation during long-term operation, and the device retains 90% of the initial PCE under a 1 sun continuous illumination exposure of 700 h.

The rise of quasi-2D Dion-Jacobson perovskites for photovoltaics

With the advance of nanotechnology, the past couple of years have witnessed the fast development of quasi two-dimensional (2D) halide perovskites, which exhibit outstanding long-term stability against moisture and heat, compared with their three-dimensional (3D) counterparts. As one of the most common structures in 2D halide perovskites, quasi-2D Dion-Jacobson (DJ) perovskites show multiple-quantum-well structures with n layers of [BX6]4- octahedral inorganic sheets sandwiched by two layers of diammonium spacers, thus exhibiting superior structural stability due to the elimination of van der Waals gaps. Thanks to the achievement of high power conversion efficiency accompanied by impressive stability, quasi-2D DJ perovskite solar cells (PSCs) have recently drawn extensive attention in the field. This review first introduces the fundamental understanding of quasi-2D DJ halide perovskites, including their superior stability, high exciton binding energy, and compositional flexibility and tunable properties. We then summarize detailed strategies to prepare high-quality quasi-2D DJ perovskites for PSCs, encompassing compositional engineering, solvent engineering, additive addition, and annealing processes. Moreover, the surface/interface modification and 2D-3D hybrid perovskite heterojunction are also discussed, for providing strategies to optimize the fabrication of quasi-2D DJ PSCs. Lastly, current challenges and perspectives toward the future development of quasi-2D DJ perovskites for photovoltaics are outlined.

Additive Engineering for Stable and Efficient Dion-Jacobson Phase Perovskite Solar Cells

Because of their better chemical stability and fascinating anisotropic characteristics, Dion-Jacobson (DJ)-layered halide perovskites, which owe crystallographic two-dimensional structures, have fascinated growing attention for solar devices. DJ-layered halide perovskites have special structural and photoelectronic features that allow the van der Waals gap to be eliminated or reduced. DJ-layered halide perovskites have improved photophysical characteristics, resulting in improved photovoltaic performance. Nevertheless, owing to the nature of the solution procedure and the fast crystal development of DJ perovskite thin layers, the precursor compositions and processing circumstances can cause a variety of defects to occur. The application of additives can impact DJ perovskite crystallization and film generation, trap passivation in the bulk and/or at the surface, interface structure, and energetic tuning. This study discusses recent developments in additive engineering for DJ multilayer halide perovskite film production. Several additive-assisted bulk and interface optimization methodologies are summarized. Lastly, an overview of research developments in additive engineering in the production of DJ-layered halide perovskite solar cells is offered.

Roles that Organic Ammoniums Play on the Surface of the Perovskite Film: A Review

The roles of organic ammonium salts (OASs) which are widely used for the surface treatment of the perovskite film, including formation of 2D perovskites, direct surface passiviation, and other effects, have been reviewed. The influencing factors for these roles of OASs are also discussed, which are important for improved efficiency and stability of perovskite solar cells. More information can be found in the Review article by X. Guo and co-workers. (DOI: 10.1002/chem.202203001).

Graded 2D/3D Perovskite Hetero-Structured Films with Suppressed Interfacial Recombination for Efficient and Stable Solar Cells via DABr Treatment

Several strategies and approaches have been reported for improving the resilience and optoelectronic properties of perovskite films. However, fabricating a desirable and stable perovskite absorber layer is still a great challenge due to the optoelectronic and fabrication limitations of the materials. Here, we introduce diethylammonium bromide (DABr) as a post-treatment material for the pre-deposited methylammonium lead iodide (MAPbI₃) film to fabricate a high-quality two-dimensional/three-dimensional (2D/3D) stacked hetero-structure perovskite film. The post-treatment method of DABr not only induces the small crystals of MAPbI₃ perovskite secondary growth into a large crystal, but also forms a 2D capping layer on the surface of the 3D MAPbI3 film. Meanwhile, the grains and crystallization of 3D film with DABr post-treatment are significantly improved, and the surface defect density is remarkably reduced, which in turn effectively suppressed the charge recombination in the interface between the perovskite layer and the charge transport layer. The perovskite solar cell based on the DABr-treatment exhibited a significantly enhanced power conversion efficiency (PCE) of 19.10% with a notable improvement in the open circuit voltage (V_OC) of 1.06 V and good stability, advocating the potential of this perovskite post-treatment approach.

Butanediammonium Salt Additives for Increasing Functional and Operando Stability of Light-Harvesting Materials in Perovskite Solar Cells

Organic diammonium cations are a promising component of both layered (2D) and conventional (3D) hybrid halide perovskites in terms of increasing the stability of perovskite solar cells (PSCs). We investigated the crystallization ability of phase-pure 2D perovskites based on 1,4-butanediammonium iodide (BDAI2) with the layer thicknesses n = 1, 2, 3 and, for the first time, revealed the presence of a persistent barrier to obtain BDA-based layered compounds with n > 1. Secondly, we introduced BDAI2 salt into 3D lead−iodide perovskites with different cation compositions and discovered a threshold-like nonmonotonic dependence of the perovskite microstructure, optoelectronic properties, and device performance on the amount of diammonium additive. The value of the threshold amount of BDAI2 was found to be ≤1%, below which bulk passivation plays the positive effect on charge carrier lifetimes, fraction of radiative recombination, and PSCs power conversion efficiencies (PCE). In contrast, the presence of any amount of diammonium salt leads to the sufficient enhancement of the photothermal stability of perovskite materials and devices, compared to the reference samples. The performance of all the passivated devices remained within the range of 50 to 80% of the initial PCE after 400 h of continuous 1 sun irradiation with a stabilized temperature of 65 °C, while the performance of the control devices deteriorated after 170 h of the experiment.

Multi-functional Strategy: Ammonium Citrate-Modified SnO2 ETL for Efficient and Stable Perovskite Solar Cells

The tin oxide (SnO₂) electron transport layer (ETL) plays a crucial role in perovskite solar cells (PSCs). However, the heterogeneous dispersion of commercial SnO₂ colloidal precursors is far from optimized, resulting in dissatisfied device performance with SnO₂ ETL. Herein, a multifunctional modification material, ammonium citrate (TAC), is used to modify the SnO₂ ETL, bringing four benefits: (1) due to the electrostatic interaction between TAC molecules and SnO₂ colloidal particles, more uniformly dispersed colloidal particles are obtained; (2) the TAC molecules distributed on the surface of SnO₂ provide nucleation sites for the perovskite film growth, promoting the vertical growth of the perovskite crystal; (3) TAC-doped SnO₂ shows higher electron conductivity and better film quality than pristine SnO₂ while offering better energy-level alignment with the perovskite layer; and (4) TAC has functional groups of C═O and N-H containing lone pair electrons, which can passivate the defects on the surface of SnO₂ and perovskite films through chemical bonding and inhibit the device hysteresis. In the end, the device based on TAC-doped ETL achieved an increased power conversion efficiency (PCE) of 21.58 from 19.75% of the reference without such treatment. Meanwhile, the PSCs using the TAC-doped SnO₂ as the ETL maintained 88% of their initial PCE after being stored for about 1000 h under dark conditions and controlled RH of 10-25%.

Halide anions engineered ionic liquids passivation layer for highly stable inverted perovskite solar cells

Long-term stability remains a great challenge for metal halide perovskite solar cells (PSCs). The utilization of ionic liquids (ILs) is a promising strategy to solve the stability problem. However, few studies have focused on controlling the halide anions of ILs, in which different organic cations can modulate the melting point of ILs and film crystal growth. Here, ILs with a 1-ethyl-3-methylimidazolium (EMIM⁺) cation and different halide anions (X = Cl, Br, and I) are employed in inverted PSCs. The results show that EMIMX can form a 1D passivation layer by the in situ growth technique and influence the surface morphology of the perovskite film. These EMIMX-treated layers simultaneously suppress the surface defects and nonradiative energy losses and improve the hydrophobic properties. As a result, a power conversion efficiency (PCE) of 20.0% is obtained for the EMIMBr-modified PSCs compared to 18.06% for the control device. Moreover, the unencapsulated devices maintain more than 90% of their initial PCE over 3000 h under ambient air, which is among the best long-term stabilities reported for NiO_x-based inverted PSCs. It also retains 74.2% and 49.5% of the initial PCE value after aging under harsher conditions, such as an 85 ± 5% relative humidity (RH) environment and at 85 °C for 48 h, respectively.

MoP2/C@rGO synthesised by phosphating the molybdenum-based metal organic framework and GO coating with excellent lithium ion storage performance

With a high specific capacity, MoP₂ has been identified as an ideal electrode material for LIBs. However, the specific capacity is negatively affected due to its poor conductivity and severe volume expansion during insertion and extraction of Li⁺. In this paper, MoP₂-C synthesized by using a Mo-MOF as a precursor, with the generation of C, can effectively solve the agglomeration problem in the synthesis process and alleviate serious volume changes during cycling. Due to the lack of carbon sources provided by a Mo-MOF, the conductivity of MoP₂-C cannot be greatly improved. Therefore, rGO and PPy are added to improve the conductivity of MoP₂ and further increase the stability of the structure. Compared with MoP₂/C and MoP₂/C@PPy, MoP₂/C@rGO exhibits the highest initial discharge specific capacity of 1208 mA h g^-1 at a current density of 100 mA g^-1 and rate performances of 830, 750, 630, 550, and 430 mA h g^-1 with the current density increasing from 100 mA g^-1 to 2000 mA g^-1. Notably, the specific capacity remains at 640 mA h g^-1 at a current density of 100 mA g^-1 after 100 cycles. Followed by 200 cycles at a current density of 2000 mA h g^-1, the specific capacity remains at 395 mA h g^-1 with a capacity retention rate of 80%.