Due to the low formation energy, surface defects are more likely to form on the surface of TiO2 films, resulting in a decline in the efficiency and stability of perovskite solar cells (PSCs). Additionally, defects on the bottom surface of the perovskite layer in contact with TiO2 play a key role in Voc (open circuit voltage) loss and the PSC degradation process. Therefore, to improve the efficiency and stability of PSCs, it is critical to develop a reproducible and low‐cost method for passivating the defects on both the TiO2 surface and on the bottom surface of the perovskite layer. In this work, fluoride is utilized as a bifacial contact passivation agent for decreasing the number of defects on the TiO2 surface and the bottom surface of the perovskite layer. PSC efficiency can be significantly increased from 21.3% to 23.7% with fluoride passivation. In addition, the long‐term stability of PSCs, especially light irradiation stability, can be markedly improved. The passivation effects of fluoride treatment on TiO2 films are studied by theoretical calculation and experimental characterization. This work provides a thorough understanding of the TiO2/perovskite interface and demonstrates an approach for improving the efficiency and stability of PSCs.

The remarkable progress in PCE can be attributed to excellent photoelectric properties of perovskites, including tunable bandgaps, high absorption coefficients, low exciton binding energies, and long carrier lifetime. [2][3][4][5] To achieve highly efficient and stable PVSCs, formamidinium (FA)-based lead triiodide perovskites have been employed as the prime light absorbers, which possess a relatively narrow bandgap (E g ≈ 1.5 eV) and promising thermal stability. [6][7][8] Consequently, various approaches have been dedicated to manipulate the crystal nucleation and grain growth for achieving high-quality perovskite films. Among these, antisolvent quenching is the most popularly used method for obtaining highly crystalline perovskite films through inducing rapid and uniform nucleation of perovskites, boosting the PCE of both conventional n-i-p and inverted p-i-n PVSCs to go beyond 25%. [9][10][11] However, the device reproductivity is limited by the narrow processing window of antisolvent dripping. [12][13][14] In addition, the commonly used antisolvents (chlorobenzene, toluene, ethyl ether etc) are quite toxic, [15][16][17] which will hinder their application in upscaling production of PVSCs.As a result, there is a strong push for searching antisolvent-free techniques to facilitate swift solvent evaporation and effective tuning of crystallization dynamics of perovskites, Developing a facile method to prepare high-quality perovskite films without using the antisolvent technique is critical for upscaling production of perovskite solar cells (PVSCs). However, the as-prepared formamidinium (FA)-based perovskite films often exhibit poor film quality with high density of defects if antisolvent is not used, limiting the photovoltaic performance and long-term stability of derived PVSCs. Herein, this work adopts presynthesized 3D methylammonium lead chloride (MAPbCl 3 ) and 1D 2-aminobenzothiazole lead iodide (ABTPbI 3 ) microcrystals into self-drying perovskite precursors, which serve as seed crystals to promote nucleation and growth of FAPbI 3 -based perovskites without requiring antisolvent extraction. The combined binary microcrystals facilitate the formation of a dense and pinhole-free perovskite film with a stable perovskite lattice and defect-healed grain boundaries, enabling efficient charge carrier transfer and reduced nonradiative recombination loss. As a result, the best-performing inverted architecture device exhibits a champion power conversion efficiency of 23.27% for small-area devices (0.09 cm 2 ) and 21.52% for large-area devices (1.0 cm 2 ). These values are among the highest efficiencies reported for antisolvent-free PVSCs. Additionally, the unencapsulated device shows enhanced moisture, thermal, and operational stabilities, and maintains 92% of its initial efficiency after being held at the maximum power point for 1000 h.

Post-treatment has been recognized as one of the effective methods for passivating the underlying defects in perovskite solar cells (PSCs), but little attention has been paid to how to pick suitable passivation agents with diverse isomers for efficient PSCs, particularly for the tin−lead (Sn−Pb) mixed PSCs. Here, we introduce the dependence of the power conversion efficiency (PCE) on a dipole moment for surface passivator screening, in which we chose three trifluoromethyl-phenylethylamine hydroiodide (CF 3 -PEAI) isomers as surface-treatment materials for hole-transport-layer-free (HTL-free) Sn−Pb mixed PSCs. The different positions of the −CF 3 group for the CF 3 -PEAI isomer result in different dipole moments, which influences the interaction between CF 3 -PEAI and lead iodide. The para position CF 3 with the highest dipole moment exhibits a higher PCE than the ortho-position with a lower dipole moment, which is attributed to the large dipole moment on the surface that could tune the surface polarity from p-type to n-type, facilitating electron charge transport in the HTL-free Sn−Pb mixed PSCs. An ultrathin 2D layer is formed on the perovskite surface to passivate the surface defects, which is responsible for the enhancement of the PCE and stability of the PSCs. As a result, the open-circuit voltage (V OC ) of the device is improved from 0.775 to 0.824 V, yielding a champion PCE of 20.17%, which is one of the highest PCEs among the reported HTL-free Sn−Pb mixed PSCs. The device also shows improved stability with remaining 75% of its initial PCEs after storage in N 2 for 700 h.

Ruddlesden−Popper (RP) perovskite solar cells (PSCs) have received increasing attention due to their promising optoelectronic properties. Herein, based on low-dimensional engineering, we employ the 1D perovskitoid BZPbI 3 (BZ = benzamidine) to tailor the (4F-PEA) 2 (FA 0.3 MA 0.7 ) 4 Pb 5 I 16 perovskite, obtaining the 1D/ 2D mixed low-dimensional perovskite with favorable phase distribution, orderly crystal orientation, and lower defect density. Furthermore, the 1D BZPbI 3 induces a large number of particles to form on the surface, considerably increasing the electrical quality and intrinsic stability of PSCs. Consequently, the 1D/2D PSCs (n = 5) reach a power conversion efficiency (PCE) approaching 20%, accompanied by improved electroluminescent external quantum efficiency. The devices show admirable long-term operational stability, retaining 85% of their initial PCE after continuous illumination at maximum power point (MPP) over 2000 h (50 ± 5 °C). This work illustrates the advantages of 1D perovskitoid in achieving efficient and stable 2D perovskite photovoltaic and other optoelectronic devices.

There have been a number of remarkable signs of progress achieved in tin–lead mixed narrow‐bandgap perovskite solar cells (PSCs) due to the high theoretical power conversion efficiency (PCE) and their promising application in tandem devices. Indeed, Sn–Pb mixed PSCs without a hole transport layer (HTL) also have been more attractive owing to lower cost and simplification of the device structure. However, the defects in perovskite film introduced by Sn2+ oxidation severely restrict device efficiency and stability.Herein, a small organic molecule, 4,4'‐sulfonyldiphenol, is employed to passivate perovskite (Eg = 1.26 eV) surface to decrease the interfacial defects and suppress the nonradiative carrier recombination. Furthermore, by regulating energy‐level alignment, charge carrier extraction is greatly facilitated. The device performance is significantly enhanced in that the champion PCE is enlarged to 21.43% with an open‐circuit voltage (Voc) of 0.876 V from only 18.02% with a Voc of 0.770 V. The stability of unencapsulated devices is improved substantially as well while retaining 80% PCE of its initial value after being stored in the glovebox for around 600 h. This facile but highly effective strategy successfully proposes the promising development of HTL‐free Sn–Pb mixed PSCs.