Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (Voc ) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced Voc deficit.

Molten-Salt-Assisted CsPbI3 Perovskite Crystallization for Nearly 20%-Efficiency Solar Cells

Aiming at stable CsPbI3 perovskite solar cells, Ge incorporated for the first time into DMAPbI3‐based precursor systems. Ge incorporation is found to be able to modify crystallization growth of CsPb1−xGexI3 films and reduce annealing temperature and treatment time by lowering CsPbI3 formation energy. The champion power conversion efficiency (PCE) of 19.52% is achieved with a certified PCE of 18.8%, which is the highest performance of CsPbI3 PSCs with alien element‐doping. In addition, in situ formation of GeO2 can passivate the grain boundary and surface defects, thus significantly improving the moisture resistance of the perovskite film and related devices. Excellent operational stability is achieved with no PCE degradation over 3000 h at a fixed bias voltage of 0.85 V under continuous white LED (6500 K) illumination and a nitrogen atmosphere. This work demonstrates that Ge‐incorporation is a promising way to stabilize CsPbI3 perovskite solar cells by simultaneously improving perovskite crystallinity and passivating the grain boundary and interfacial defects.

Ge Incorporation to Stabilize Efficient Inorganic CsPbI3 Perovskite Solar Cells

Recently, all-inorganic CsPbX3 perovskite solar cells have stimulated enormous research interests due to their numerous merits including superior thermal and light stability and become one of the most prominent research...

Crystallization Kinetics Modulation and Defects Suppression of All-Inorganic CsPbX3 Perovskite Film

CsPbI3 inorganic perovskites have attracted significant attention due to their desirable bandgap for tandem solar cells and excellent thermal stability. However, CsPbI3 perovskite solar cells (PSCs) still exhibit low efficiency and high energy loss due to nonradiative recombination. Herein, functionalized Ti3C2Fx quantum dots (QDs) are prepared and selected as interface passivators to enhance the performance of CsPbI3 PSCs. The systematic experimental results reveal that Ti3C2Fx QDs serve as effective passivators mainly in three aspects: 1) p‐type Ti3C2Fx QDs can tune the energy level of perovskite films and provide an efficient pathway for hole transfer; 2) Ti3C2Fx QDs can effectively passivate defects and reduce interfacial nonradiative recombination, and 3) Ti3C2Fx QDs form a barrier layer to prevent water invasion and improve the stability of CsPbI3 PSCs. Consequently, the champion CsPbI3 PSC with Ti3C2Fx QDs treatment exhibits an excellent efficiency of 20.44% with a high open‐circuit voltage of 1.22 V. Meanwhile, the corresponding device without encapsulation retained 93% of its initial efficiency after 600 h of storage in ambient air.

Fluorine Functionalized MXene QDs for Near‐Record‐Efficiency CsPbI3 Solar Cell with High Open‐Circuit Voltage

Defects in CsPbX3 Perovskite: From Understanding to Effective Manipulation for High-Performance Solar Cells

Enhanced Efficiency of Inorganic CsPbI3−xBrx Perovskite Solar Cell via Self-Regulation of Antisite Defects

The existence of high defect density in the interface region limits further promotion of perovskite photovoltaic performance and long-term stability. Surface termination of perovskite films alters the interfacial electronic states, which are responsible for the carrier dynamics and physical and chemical properties of the interface. Therefore, suitable termination design is beneficial to the photoelectric performance and operational stability. Here, guanidinium thiocyanate (GASCN) was selected to modify the surface terminations of methylamine lead iodide (MAPbI3) perovskite films by taking advantage of its strong bonding capacity and increased hydrogen-bonding interactions with the [PbI6]4− octahedron. Firstly, to select an effective solvent to introduce GASCN onto the surface of MAPbI3, multiple solvents with varied polarity were tested to carefully examine their effects on the perovskite active layer in consideration of their scouring or polar erosion effect. Secondly, the surface matrix is formed after thermal annealing due to the strong chemical bonding between GA+ and the perovskite surface. The strong surface bonding immobilizes the anion (I−) and reduces its migration, so suppressing the hysteresis behavior of the assembled device. As well, the surface matrix blocks invasion of moisture and oxygen from the atmosphere and thus improves the long-term stability of assembled devices.

Design of surface termination for high-performance perovskite solar cells

Nonradiative losses caused by defects are the main obstacles to further advancing the efficiency and stability of perovskite solar cells (PSCs). There is focused research to boost the device performance by reducing the number of defects and deactivating defects; however, little attention is paid to the defect‐capture capacity. Here, upon systematically examining the defect‐capture capacity, highly polarized fluorinated species are designed to modulate the dielectric properties of the perovskite material to minimize its defect‐capture radius. On the one hand, fluorinated polar species strengthen the defect dielectric‐screening effect via enhancing the dielectric constant of the perovskite film, thus reducing the defect‐capture radius. On the other, the fluorinated iodized salt replenishes the I‐vacancy defects at the surface, hence lowering the defect density. Consequently, the power‐conversion efficiency of an all‐inorganic CsPbI3 PSC is increased to as high as 20.5% with an open‐circuit voltage of 1.2 V and a fill factor of 82.87%, all of which are among the highest in their respective categories. Furthermore, the fluorinated species modification also produces a hydrophobic umbrella yielding significantly improved humidity tolerance, and hence long‐term stability. The present strategy provides a general approach to effectually regulate the defect‐capture radius, thus enhancing the optoelectronic performance.

Polar Species for Effective Dielectric Regulation to Achieve High‐Performance CsPbI3 Solar Cells

Solar cell efficiency and stability are two key metrics to determine whether a photovoltaic device is viable for commercial applications. The surface termination of the perovskite layer plays a pivotal role in not only the photoelectric conversion efficiency (PCE) but also the stability of assembled perovskite solar cells (PSCs). Herein, a strong chelate coordination bond is designed to terminate the surface of the perovskite absorber layer. On the one hand, the ligand anions bind with Pb cations via a bidentate chelating bond to restrict the ion migration, and the chelate surface termination changes the surface from hydrophilic to hydrophobic. Both are beneficial to improving the long‐term stability. On the other hand, the formation of the chelating bonding effectively eliminates the deep‐level defects including PbI and Pb clusters on the Pb‐I and FA‐I terminations, respectively, as confirmed by theoretical simulation and experimental results. Consequently, the PCE is increased to 24.52%, open circuit voltage to 1.19 V, and fill factor to 81.53%; all three are among the highest for hybrid perovskite cells. The present strategy provides a straightforward means to enhance both the PCE and long‐term stability of PSCs.

Yuankun Fang

Papers

Molten-Salt-Assisted CsPbI3 Perovskite Crystallization for Nearly 20%-Efficiency Solar Cells

Enhanced Efficiency of Inorganic CsPbI3−xBrx Perovskite Solar Cell via Self-Regulation of Antisite Defects

Design of surface termination for high-performance perovskite solar cells

Polar Species for Effective Dielectric Regulation to Achieve High‐Performance CsPbI3 Solar Cells

Chelate Coordination Strengthens Surface Termination to Attain High‐Efficiency Perovskite Solar Cells