stability of perovskite materials under photo-, thermal, or moisture stresses, and the volatile nature of the organic cations in the prototype (organic-inorganic hybrid) perovskite composition, may hinder their commercialization. [3][4][5] To address the stability issues, all-inorganic perovskite solar cells (PVSCs) based on cesium (Cs) lead halide has been developed and has drawn considerable research attention, wherein the organic cations in the perovskite structure are completely replaced by the inorganic Cs ions, whose atomic size is suitable to form the perovskite crystal structure. [6][7][8][9] Among all the Cs-based PVSCs, the cesium lead iodine (CsPbI 3 ) has the most favorable bandgap (1.73 eV), but the black phase of CsPbI 3 is not stable at room temperature. [10,11] Therefore, various methods have been investigated including partially substituting I or Pb ions in the CsPbI 3 perovskite with Br or Sn ions, which regulates the tolerance factor of the lattice and thus improves the phase stability of blackphase CsPbI 3 . [12][13][14][15] Among them, CsPbI 2 Br shows good phase stability and a reasonable bandgap of 1.92 eV, which is suitable for perovskite/silicon tandem cells applications. [10,16,17] At present, PCE of over 19% has been reported for allinorganic PVSCs that employed the doped Spiro-OMeTAD as Designing new hole-transporting materials (HTMs) with desired chemical, electrical, and electronic properties is critical to realize efficient and stable inverted perovskite solar cells (PVSCs) with a p-i-n structure. Herein, the synthesis of a novel 3D small molecule named TPE-S and its application as an HTM in PVSCs are shown. The all-inorganic inverted PVSCs made using TPE-S, processed without any dopant or post-treatment, are highly efficient and stable. Compared to control devices based on the commonly used HTM, PEDOT:PSS, devices based on TPE-S exhibit improved optoelectronic properties, more favorable interfacial energetics, and reduced recombination due to an improved trap passivation effect. As a result, the all-inorganic CsPbI 2 Br PVSCs based on TPE-S demonstrate a remarkable efficiency of 15.4% along with excellent stability, which is the one of the highest reported values for inverted all-inorganic PVSCs. Meanwhile, the TPE-S layer can also be generally used to improve the performance of organic/inorganic hybrid inverted PVSCs, which show an outstanding power conversation efficiency of 21.0%, approaching the highest reported efficiency for inverted PVSCs. This work highlights the great potential of TPE-S as a simple and general dopant-free HTM for different types of high-performance PVSCs.
