No abstract

High-crystalline-quality wide-bandgap metal halide perovskite materials that achieve superior performance in perovskite solar cells (PSCs) have been widely explored. Precursor concentration plays a crucial role in the wide-bandgap perovskite crystallization process. Herein, we investigated the influence of precursor concentration on the morphology, crystallinity, optical property, and defect density of perovskite materials and the photoelectric performance of solar cells. We found that the precursor concentration was the key factor for accurately controlling the nucleation and crystal growth process, which determines the crystallization of perovskite materials. The precursor concentration based on Cs0.05FA0.8MA0.15Pb(I0.84Br0.16)3 perovskite was controlled from 0.8 M to 2.3 M. The perovskite grains grow larger with the increase in concentration, while the grain boundary and bulk defect decrease. After regulation and optimization, the champion PSC with the 2.0 M precursor concentration exhibits a power conversion efficiency (PCE) of 21.13%. The management of precursor concentration provides an effective way for obtaining high-crystalline-quality wide-bandgap perovskite materials and high-performance PSCs.

With the rapid development of power conversion efficiency (PCE) up to 25.7%, perovskite solar cells (PSCs) have been considered a promising photovoltaic technology. [1][2][3][4] It is reported that the theoretical PCE of PSCs is more than 30%, which suggests that there is still much room for further improvement. [5] However, the nonradiative recombination in PSCs has a severe impact on the open-circuit voltage (V OC ), which needs to be carefully addressed. [6] Deep-level defects in perovskite films are the predominant sources of defectassisted nonradiative recombination losses. [7] Hence, it is necessary to develop an effective strategy to reduce the intrinsic defects including interstitials, vacancies, antisites, and so on.Defect passivation is considered the most direct approach to boost V OC and PCE by minimizing nonradiative recombination, which is widely used in the field of PSCs. [7,8] The reported works demonstrated that the defect states are mainly located at the surface and interfacial grain boundaries of perovskite films. [9] Thus, it is supposed to be an effective method to passivate defects by utilizing appropriate materials as the additive. Organic functional groups such as phenylethylammonium (PEA þ ), 1,4-butanediammonium (BDA þ ), and guanidinium (GA þ ) are widely used for defect passivation in PSCs. [10][11][12] Jiang et al. demonstrated that PEAI could obtain a higher efficiency device by suppressing nonradiative recombination. [13] In PEAI materials, the benzene ring π-conjugation structure reduces the neutral iodine related defects, and the amine group forms hydrogen bonds with iodide ions. [13] Zhang et al. proposed using GA þ as a post-treatment reagent, leading to an increase of more than 50% in PCE of quasi-2D PSCs from 8.62% to 13.13%. [14] It has been reported that adjusting the polarity of passivation molecules through structural design can effectively improve the adsorption capacity between passivation molecules and defect sites, ensuring passivators fully interact with the defect sites. [15] Tan et al. used 4-trifluoromethyl-phenylammonium (CF3-PA) as the passivator, which exhibits a stronger polarity than the wildly used PEAI, leading to a reliable perovskite surface-passivator interaction. [16] Through the improved grain surface passivation with CF3-PA, the PCE of Pb-Sn PSCs and all perovskite tandem solar cell is as high as 22% and 26.4%, respectively. [16] As a type of polycrystalline film, the defect density in perovskite film is closely related to its growth process.

Surface passivation by constructing 2D/3D structure is considered as an effective strategy to suppress non-radiative recombination and improve device efficiency and stability. Herein, the 2D perovskite is in-situ formed on...

Earth‐abundant LaFeO3 is a promising p‐type semiconductor for photoelectrochemical cells due to its stable photoresponses, high photovoltages and appropriate band alignments, but the photoelectrochemical properties of LaFeO3, especially the incident‐photon‐to‐current conversion efficiency, need to be further improved. Herein, we propose to partially substitute La3+ of LaFeO3 with Ag+ to enhance the photoelectrochemical performance of LaFeO3. The combined experimental and computational studies show that Ag‐substitution improves surface charge transfer kinetics through introducing active electronic states and increasing electrochemically active surface areas. Furthermore, Ag‐substitution decreases grain boundary number and increases majority carrier density, which promotes bulk charge transports. Ag‐substitution also reduces the bandgap energy, increasing the flux of carriers involved in photoelectrochemical reactions. As a result, after 8 % Ag‐substitution, the photocurrent density of LaFeO3 is enhanced by more than 6 times (−0.64 mA cm−2 at 0.5 V vs RHE) in the presence of oxygen, which is the highest photocurrent gain compared with other cation substitution or doping. The corresponding photocurrent onset potential also demonstrates a positive shift of 30 mV. This work highlights the versatile effects of Ag‐substitution on the photoelectrochemical properties of LaFeO3, which can provide useful insights into the mechanism of enhanced photoelectrochemical performance by doping or substitution.