Alkali Metal Fluoride-Modified Tin Oxide for n-i-p Planar Perovskite Solar Cells

Composite SnO2-K2S ETL for energy level regulation and electron mobility enhancement in perovskite solar cells

High-performance perovskite solar cells commonly utilize SnO2 as the electron transport layer (ETL), which is vital for perovskite crystallization and defect regulation, yet energy level mismatch, oxygen vacancies in SnO2, and defects at the buried interface impede the device's photovoltaic performance. Therefore, we found that incorporating K2S into the SnO2 layer effectively regulated the energy levels and occupied oxygen vacancies, enhancing the electron mobility of the composite SnO2-K2S ETL and improving the interface quality to promote efficient electron extraction and transport. Consequently, the device based on SnO2-K2S ETL showed an enhanced photovoltaic performance with power conversion efficiency of to 23.28%.

Intermediate-Controlled Synthesis of Quasi-2D (PEA)2MA4Pb5I16 in the 20-30% Relative Humidity Glovebox Environment for Fabricating Perovskite Solar Cells with 1 Month Durability in the Air

Herein, quasi-two-dimensional (Q-2D) (PEA)2MA4Pb5I16 (prepared by a two-step process) and hole transport layer of a solar cell were fabricated in a high relative humidity (25 ± 5%) environment. The PSC behavior of most Q-2D perovskites is worse than that of three-dimensional perovskites owing to the horizontal alignment of the innate characteristic organic plates on the substrate. Using hybrid immersion solvents (HISs), we have improved vertical alignment in an appropriate ratio to enhance the efficiency of charge transfer and the high coverage of the first priming layer (first step). The grazing incidence X-ray diffraction pattern of the optimized structures revealed a preferential orientation for the vertical alignment of (111), which improved the charge transfer in PSCs and micrometer-level grain size growth. The second step was processed in a high-humidity environment (50 ± 5%) (methylammonium iodide solution embedded), and Q-2D (PEA)2MA4Pb5I16 demonstrated distinct grain boundaries. The power conversion efficiency (PCE, 13.09%) of the champion device of the first priming layer prepared using the HIS system increased by >55% compared to the single-immersion solvent (8.3%). The PCE of the ion-modified ETL PSCs was 16.02% (CsF-3) and 14.58% (CsCl-3) and demonstrated 22 and 11% improvement, respectively. The ion-modified electron transport layer (ETL) was deposited in the air, which reduced the power consumption of preparing perovskite solar cells (PSCs). Finally, all Q-2D PSCs were stored in the air, and three PSCs (DMF/DMSO, CsF-3, and CsCl-3) using HIS exhibited long-term stability for 1 month maintaining 80-88% of PCE, demonstrating the importance of the HIS system to improve the first step of growth orientation, which enhances the stability and photovoltaic properties of PSCs.

High efficiency and stability of perovskite solar cells prepared by alkali metal interfacial modification

Perovskite solar cells (PSCs) have attracted much attention at home and abroad due to their excellent photoelectric properties. Defects in the electron transport layer (ETL) and ETL/perovskite interface greatly affect the power conversion efficiency (PCE) and stability of PSCs. In the paper, the surface of tin dioxide (SnO2) ETL was modified by an alkali metal salt (NaBr, KBr, and RbBr) solution to optimize electron transport and passivate SnO2/perovskite. The results show that the photovoltaic performance of the PSCs is significantly improved after interfacial modification, especially the KBr-modified PSC has the highest PCE, which is 7.8% higher than that of the unmodified device, and the open-circuit voltage, short-circuit current density and fill factor are all greatly improved. This improvement is attributed to the fact that interfacial modification reduces the trap density of the SnO2 films, increases the mobility of the SnO2 films film, effectively passivates defects, and significantly inhibits the recombination at the SnO2/perovskite interface. This method aims to use simple and low-cost inorganic materials for effective interface modification.

Enhancing Stability and Performance in Tin-Based Perovskite Field-Effect Transistors Through Hydrogen Bond Suppression of Organic Cation Migration

Ion migration poses a substantial challenge in perovskite transistors, exerting detrimental effects on hysteresis and operational stability. This study focuses on elucidating the influence of ion migration on the performance of tin-based perovskite field-effect transistors (FETs). It is revealed that the high background carrier density in FASnI3 FETs arises not only from the oxidation of Sn2+ but also from the migration of FA+ ions. The formation of hydrogen bonding between FA+ and F- ions efficiently inhibits ion migration, leading to a reduction in background carrier density and an improvement in the operational stability of the transistors. The strategy of hydrogen bond is extended to fluorine-substituted additives to improve device performance. The incorporation of 4-fluorophenethylammonium iodide additives into FETs significantly minimizes the shift of turn-on voltage during cyclic measurements. Notably, an effective mobility of up to 30 cm2 V-1 s-1 with an Ion/off ratio of 107 is achieved. These findings hold promising potential for advancing tin-based perovskite technology in the field of electronics.

Facile NaF Treatment Achieves 20% Efficient ETL-Free Perovskite Solar Cells

Electron transporting layer (ETL)-free perovskite solar cells (PSCs) exhibit promising progress in photovoltaic devices due to the elimination of the complex and energy-/time-consuming preparation route of ETLs. However, the performance of ETL-free devices still lags behind conventional devices because of mismatched energy levels and undesired interfacial charge recombination. In this study, we introduce sodium fluoride (NaF) as an interface layer in ETL-free PSCs to align the energy level between the perovskite and the FTO electrode. KPFM measurements clearly show that the NaF layer covers the surface of rough underlying FTO very well. This interface modification reduces the work function of FTO by forming an interfacial dipole layer, leading to band bending at the FTO/perovskite interface, which facilitates an effective electron carrier collection. Besides, the part of Na⁺ ions is found to be able to migrate into the absorber layer, facilitating enlarged grains and spontaneous passivation of the perovskite layer. As a result, the efficiency of the NaF-treated cell reaches 20%, comparable to those of state-of-the-art ETL-based cells. Moreover, this strategy effectively enhances the operational stability of devices by preserving 94% of the initial efficiency after storage for 500 h under continuous light soaking at 55 °C. Overall, these improvements in photovoltaic properties are clear indicators of enhanced interface passivation by NaF-based interface engineering.

Alkali Metal Cations Modulate the Energy Level of SnO2 via Micro-agglomerating and Anchoring for Perovskite Solar Cells

N-type tin oxide (SnO₂) films are commonly used as an electron transport layer (ETL) in perovskite solar cells (PSCs). However, SnO₂ films are of poor quality due to facile agglomeration under a low-temperature preparation method. In addition, energy level mismatch between the SnO₂ and perovskite (PVK) layer as well as interfacial charge recombination would cause open-circuit voltage loss. In this work, alkali metal oxalates (M-Oxalate, M = Li, Na, and K) are doped into the SnO₂ precursor to solve these problems. First, it is found that the hydrolyzed alkali metal cations tend to change colloid size distribution of SnO₂, in which Na-Oxalate with suitable basicity leads to most uniform colloid size distribution and high-quality SnO₂-Na films. Second, the electron conductivity is enhanced by slightly agglomerated SnO₂-Na, which facilitates the transmission of electrons. Third, alkali metal cations increase the conduction band level of SnO₂ in the sequence of K⁺, Na⁺, and Li⁺ to promote band alignment between ETLs and perovskite. Based on the optimized film quality and energy states of SnO₂-Na, the best PSC efficiency of 20.78% is achieved with a significantly enhanced open-circuit voltage of 1.10 V. This work highlights the function of alkali metal salts on the colloid particle distribution and energy level modulation of SnO₂.