SOLAR CELLS. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange.

Solar Cells Most efforts to grow superior films of organic-inorganic perovskites for solar cells have focused on methylammonium lead iodide (MAPbI3). However, formamidinium lead iodide (FAPbI3) has a broader solar absorption spectrum that could ultimately lead to better performance. Yang et al. grew high-quality FAPbI3 films by starting with a film of lead iodide and dimethylsulfoxide (DMSO) and then exchanging the DMSO with formamidinium iodide. Their best devices achieved power conversion efficiencies exceeding 20%. Science , this issue p. [1234][1] [1]: /lookup/doi/10.1126/science.aaa9272

Shallow Iodine Defects Accelerate the Degradation of α-Phase Formamidinium Perovskite

Formamidinium lead iodide (FAPbI3) is one of the most extensively studied perovskite materials due to its narrow band gap and high absorption coefficient, which makes it highly suitable for optoelectronic applications. Deposition of a solution containing lead iodide (PbI2) and formamidinium iodide (FAI) or sequential deposition of PbI2 and FAI usually leads to the formation of films with a poor morphology and an unstable crystal structure that readily crystallize into two different polymorphs: the photoinactive yellow phase and the photoactive black phase. In this work, 2D 2-phenylethylammonium lead iodide (PEA2PbI4) thin films are deposited by a scalable doctor-blade coating technique and used as a growth template for the high-quality 3D FAPbI3 perovskite thin films which are obtained by organic cation exchange. We report the structural, morphological and optical properties of these converted 3D FAPbI3 perovskite films which we compare to the directly deposited 3D FAPbI3 films. The converted FAPbI3 thin films are compact, smooth, and highly oriented and exhibit better structural stability in comparison with the directly deposited 3D films. These results not only underscore the importance of the employed deposition techniques in fabricating highly crystalline and stable perovskite thin films but also provide a strategy to easily obtain very compact perovskite layers using doctor-blade coating.

Dual-Resistance of Ion Migration and Moisture Erosion via Hydrolytic Crosslinking of Siloxane Functionalized Poly(Ionic Liquids) for Efficient and Stable Perovskite Solar Cells

Summary Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm−2, presenting an important breakthrough in PeLEDs.

In this work, thin film perovskite solar cells with different compositions have been manufactured with the help of the methods: spin coating, spray pyrolysis, etching, sputtering, chemical bath deposition, flash evaporation and chemical vapor deposition (CVD). The solar cells and their materials have been characterized electrically at the solar simulator setup, respectively through UV/Vis absorption spectroscopy, photoluminescence (PL), scanning electron microsco-py (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). In a classical approach, which has been optimized within our Surface Science group, a two-step spin coating and chemical bath deposition method for producing the perovskite material methylammonium lead iodide (MAPI) was used in this work to manufacture Glass/FTO/c-TiO2/m-TiO2/MAPI/spiro-MeOTAD/Au solar cells, having a maximum power conversion efficiency (PCE) of 15,6 %, with a solar cell dimension of 32,5 mm2 and a mini-module substrate dimension of 4 cm2. In a next approach, a one-step spin coating and antisolvent method was used according to literature1 to deposit a thin film of a triple cation, double anion lead perovskite: (CsaMAbFAc)1PbIxBr3-x. This approach is used to compare the performance of solar cells made using our lab methods and the production of our own stack of materials Glass/FTO/c-TiO2/m-TiO2/(CsaMAbFAc)1PbIxBr3-x/spiro-MeOTAD/Au with those in literature. While according to literature1 the published per-ovskite recipe reached a maximum PCE of over 20% in the authors’ labs, a maximum efficiency of 18,5 % could be obtained within this work. A further increase in efficiency is discussed with respect to our solar simulator measurement method. Furthermore, a flash evaporation setup has been built and employed in a novel solvent-free approach to produce films of the alterna-tive perovskite material for solar cells, methylammonium tin iodide (MASI), which uses tin (Sn) instead of the widely used lead (Pb). These experiments show that the flash evaporation pro-cess can produce MASI films of a high chemical purity. Additionally, a new chemical vapor deposition (CVD) setup has been built and used to test a variety of precursor combinations for synthesizing methylammonium lead iodide (MAPI), formamidinium lead iodide (FAPI), or hy-drogen lead iodide (HPbI3). For producing MAPI perovskite films, methylamine gas (MA) and home-made hydrogen iodide (HI) gas were successfully used. For these reactions, the mecha-nism has been clarified using XPS and XRD. The best solar cell built using the up-scalable CVD setup shows an efficiency of 12,9 %.

The greatest remaining barrier to the commercialization of perovskite solar cells is their instability to ambient environmental conditions. While most studies of the electronic stability of perovskites employ finished devices, we here exploit the contactless characterization technique time-resolved microwave conductivity to probe electronic properties in the absence of encapsulation and interface effects. By tracking the mobility of charge carriers in two archetypal perovskite compounds, methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3) under various conditions, we are able to make decisive statements about the role of water in the electronic performance of perovskites. Overall, we observe a strong negative correlation between hydration and mobility in MAPbI3, but not in FAPbI3. We anticipate that the data presented herein will serve as a valuable resource in future stability studies in perovskite solar cells and, ultimately, lead to more stable devices.

This study introduces a simple and effective way to control the bandgap of perovskite film by constructing bilayer film composed of methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3) layers. The bilayer film is fabricated through the sequential co-deposition of methylammonium iodide (MAI) and lead iodide (PbI2), followed by formamidinium iodide (FAI) and PbI2. Interestingly, the bandgap of the bilayer film can be tuned from 1.60 to 1.51eV by adjusting the thickness of each layer. X-ray photoelectron spectroscopy (XPS) indicates that the highly diffusive methylammonium ions (MA+) enables the formation of stable α-phase with formamidinium ions (FA+) in the bilayer perovskite film even without further thermal annealing. Bilayer film-based perovskite solar cells (PSCs) are fabricated through an all-vacuum deposition process. The bilayer PSC exhibits higher power conversion efficiency (PCE) of 17.0% compared to the single-layer PSC based on MAPbI3 or FAPbI3.

It is well established that the lack of understanding the crystallization process in two-step sequential deposition has a direct impact on efficiency, stability and reproducibility of perovskite solar cells. Here, we try to understand the solid-solid phase transition occuring during two-step sequential deposition of methylammonium lead iodide and formamidinium lead iodide. Using metadynamics, X-ray diffraction and Raman spectroscopy, we reveal the microscopic details of this process. We find that the formation of perovskite proceeds through intermediate structures and report polymorphs found for methylammonium lead iodide and formamidinium lead iodide. From simulations, we discover a possible crystallization pathway for the highly efficient metastable α-phase of formamidinium lead iodide. Guided by these simulations, we perform experiments that results in the room temperature crystallization of α-formamidinium lead iodide.

It is well established that the lack of understanding the crystallization process in a two-step sequential deposition has a direct impact on efficiency, stability, and reproducibility of perovskite solar cells. Here, we try to understand the solid-solid phase transition occurring during the two-step sequential deposition of methylammonium lead iodide and formamidinium lead iodide. Using metadynamics, x-ray diffraction, and Raman spectroscopy, we reveal the microscopic details of this process. We find that the formation of perovskite proceeds through intermediate structures and report polymorphs found for methylammonium lead iodide and formamidinium lead iodide. From simulations, we discover a possible crystallization pathway for the highly efficient metastable α phase of formamidinium lead iodide. Guided by these simulations, we perform experiments that result in the low-temperature crystallization of phase-pure α-formamidinium lead iodide.

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

The rapid reaction between lead iodide (PbI2) and formamidinium iodide (FAI) complicates the fabrication of high‐quality formamidinium lead iodide (FAPbI3) films. Conventional methods, such as using nonvolatile small molecular additives to slow the reaction, often result in buried interfacial voids and molecule diffusion, compromising the devices’ operational stability. In this study, we introduced a molecular “thruster”—a hypervalent iodine (III) compound with three carbonyl groups and a C−−I+ bond—that possesses coordination and dissociation abilities, enabling programed modulation of perovskite‐film growth kinetics. Initially, the three carbonyl groups coordinate with PbI2 to slow the reaction between FAI and PbI2, preventing δ‐phase formation. As temperature rises, the C−−I+ bond dissociates, promoting perovskite growth and the dissociated product iodobenzene will promote solvent volatilization, thus avoiding buried interfacial voids. Another product, a carbene compound with eight lone pair electrons sufficiently passivate the undercoordinated Pb2+ defects and anchors at grain boundaries without diffusion. Consequently, the resultant FAPbI3 film displays high‐quality with enhanced phase purity, compact morphology, and reduced defects. Evidently, 0.062‐ and 1.004‐cm2 pero‐SCs achieve power conversion efficiencies (PCEs) of up to 26.06 % (25.79 % certified) and 24.65 %, respectively. This approach also controls perovskite‐film growth on plastic substrates, resulting in flexible pero‐SCs with an impressive PCE of 25.12 %.

Cation engineering on lead iodide perovskites for stable and high-performance photovoltaic applications

Here, we show that flexible perovskite solar cells (PSCs) with high operational stability and power conversion efficiency (PCE) approaching 20% were achieved by elastic grain boundary (GB) encapsul...

Formamidinium iodide (FAI) based perovskite solar cells (PSCs) have now been established as effective PSCs than methylammonium lead iodide perovskite for several years due to their optimal bandgap and high thermal stability. However, the FAI-based PSCs have humidity issues, due to which mixed cation perovskites are getting popular. MAI-based PSCs have better stability against high humidity but low thermal stabilities. Herein, we prepared highly crystallized, efficient, and large-grain size perovskite films via FAI post-dripping process. In addition, the most promising structures FAI mixed MAPbI3 were explored as stable and effective active layers. The post-dripping of FAI solution just after the MAPbI3 deposition provides a robust long-distance diffusion, long carrier life, and enhanced grain sizes when compared to MAPbI3 PSCs. Based on the facile way of mixed cation perovskite preparation by post-dripping, the power conversion efficiency (PCE) has risen from 15.24% to 17.52% in comparison with the pristine devices. This results in the best quality and large grain perovskite films which enhanced the PSCs' performance by reducing defect density and regulating the crystallization rate.