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

Abstract

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.

Small Molecules Functionalized Zinc Oxide Interlayers for High Performance Low‐Temperature Carbon‐Based CsPbI2Br Perovskite Solar Cells

“…This phenomenon could be ascribed to the formation of interfacial dipole mentioned above, which is expected to decrease the W F value of ZnO film by bending vacuum energy level. [ 40,53 ] Indeed, the UPS results of doped ZnO films exhibited the lower W F values, as further confirmed by Kelvin probe force microscopy (KPFM). As shown in Figure S14, Supporting Information, the doped ZnO films presented larger contact potential difference (CPD) than that of reference one, which means decreased W F values.…”

One-Stone-for-Two-Birds Method to Improve the SnO2 Layers for High Power-per-Weight Flexible Perovskite Solar Cell Mini-modules

“…Besides bringing a change in the SnO 2 film surface species, the introduction of PAAm would alter the energetic characteristic of the film owing to the evolution of oxygen vacancies. As shown in Figure S8, we first checked the change in the optical bandgap . To determine the effect of PAAm on the energetic band structure of SnO 2 , we performed UPS measurements on different SnO 2 films.…”

“…As shown in Figure S8, we first checked the change in the optical bandgap. 37 To determine the effect of PAAm on the energetic band structure of SnO 2 , we performed UPS measurements on different SnO 2 films. As shown in Figure 3a the energy barrier and enhancing the charge collection efficiency at the SnO 2 /perovskite interface.…”

Improving Thermal Stability of High-Efficiency Methylammonium-Free Perovskite Solar Cells via Chloride Additive Engineering

“…Diverse functional groups present on these monolayers, including amines, siloxanes, and sulfydryl, have the capability to bind with tin atoms, initiating the reconstruction of the SnO 2 surface. − Compared to interface modification strategies, the preburying additive strategy offers a simpler approach, allowing simultaneous modification of both the perovskite and SnO 2 ETL . The treatment of SnO 2 with pre-embedded ionic salts, especially ammonium salts and alkali halide salts, has been demonstrated as a readily implemented and effective additive strategy. ,, This effectiveness is attributed to the capacity of the cationic and anionic species within the salts to effectively neutralize positively and negatively charged defects via strong hydrogen bonding and electrostatic forces. , Simultaneously, halide anions (such as Cl – and F – ) can substitute for perovskite defect sites and introduce into SnO 2 , suppressing unnecessary ion migration and nonradiative recombination. ,, Wang et al documented the intrinsic doping of Cl in SnO 2 nanocrystals (NCs) with MACl, which proficiently mitigated energy barriers and diminished the number of traps at the concealed boundary between the perovskite and ETL. This strategy, relying on the stability of PSCs featuring Cl-doped SnO 2 NCs, yielded an efficiency of 25.03% in miniature cells, showcasing exceptional stability under varying environmental and lighting conditions.…”