A gradient heterosturcture is one of the basic methods to control the charge flow in perovskite solar cells (PSCs). However, a classical route for gradient heterosturctures is based on the diffusion technique, in which the guest ions gradually diffuse into the films from a concentrated source of dopants. The gradient heterosturcture is only accessible to the top side, and may be time consuming and costly. Here, the “intolerant” n‐type heteroatoms (Sb3+, In3+) with mismatched cation sizes and charge states can spontaneously enrich two sides of perovskite thin films. The dopants at specific sides can be extracted by a typical hole‐transport layer. Theoretical calculations and experimental observations both indicate that the optimized charge management can be attributed to the tailored band structure and interfacial electronic hybridization, which promote charge separation and collection. The strategy enables the fabrication of PSCs with a spontaneous graded heterojunction showing high efficiency. A champion device based on Sb3+ doped film shows a stabilized power‐conversion efficiency of 21.04% with a high fill factor of 0.84 and small hysteresis.

tuning strategy [14,15] with improved moisture tolerance. On the other hand, we have first demonstrated a surface functionalization method of MAPbI 3 (MA = CH 3 NH 3 + ) film with tetra-alkyl ammonium molecules which could tremendously enhance the humid stability of the perovskite device even under very harsh condition (90% relative humidity). [16] Furthermore, a series of hydrophobic molecules, such as alkylphos phonic acid ω-ammonium chloride, [17] dodecyltrimethoxysilane (C 12 -silane), [18] polystyrene, [19,20] polymethyl methacrylate, [21] and phenylethylammonium iodide, [22] were developed to enhance the moisture tolerance of perovskites. In addition, encapsulation was another effective way to protect perovskites form degradation induced by ambient moisture. [23][24][25][26] However, it was found that the organic layers with insulated alkyl groups usually limit the carrier extraction and thus result in slight loss of PCEs in our experiments.To protect the perovskite devices with high efficiency, surface-functionalized molecules must combine excellent electrical conductivity and hydrophobic properties. Among various molecules, thiophene derivatives enable the electron-rich conjugated π system, which consist of four 2p orbital electrons from carbon atoms and two lone electron pairs from sulfur atom. [27] These thiophene-based derivatives or polythiophene derivatives are usually used as sufficient hole extraction materials, together with the advantage of their highest occupied molecular orbital (HOMO). [28] Moreover, unlike siloxanes and amines, thiophenes can be directly coordinated to the lead atom by the lone pair of electrons offered by the sulfur atom, which may be directly interacted with the valance band of perovskite. [29] Therefore, if we modify perovskite surface with such molecules, device with high efficiency and stability is expected.In this work, we reported a new strategy to fabricate moisturetolerant and high-performance PSCs by employing 3-alkylthiophene derivatives as the multifunctional surface layer. This class of molecules contains unique delocalized conjugated π systems and hydrophobic alkyl groups that can enhance the charge transfer at perovskite/2,2′-7,7′-tetrakis[N,N-di(4-methoxyphenyl) amino]-9,9′-spirobifluorene (Spiro-OMeTAD) interface and protect the inner perovskite. Planar heterojunction devices utilizing Although the efficiency of perovskite solar cells (PSCs) is close to crystalline silicon solar cells, the instability of perovskite, especially in humid condition, still hinders its commercialization. As an effective method to improve their stability, surface functionalization, by using hydrophobic molecules, has been extensively investigated, but usually accompanied with the loss of device efficiencies owing to their intrinsic electrical insulation. In this work, for the first time, it is demonstrated that 3-alkylthiophene-based hydrophobic molecules can be used as both water-resistant and interface-modified layers, which could simultaneously enhance both stability and perform...

In this paper, oleylammonium polysulfides molecules were self-assembled on an etched perovskite film, leading to an enhancement in moisture stability of the devices.

A highly transparent NiO layer was prepared by a solution processing method with nickel(II) 2-ethylhexanoate in non-polar solvent and utilized as HTM in perovskite solar cells. Excellent optical transmittance and the matched energy level lead to the enhanced power conversion efficiency (PCE, 18.15 %) than that of conventional sol-gel-processed NiO-based device (12.98 %).