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The carrier recombination loss induced by defects, imperfect contact and energy level barriers at the buried interface severely restricts the greater advancement of comprehensive performance of perovskite solar cells (PSCs). Herein, a versatile inorganic ammonium salt of diammonium hydrogen phosphate (DAP) is exploited as a "double-sided tape" modifier to be deposited at the TiO2/perovskite buried interface, which not only passivates the surface defects of TiO2 and perovskite layers and simultaneously bridges the two films via the chemical reactions of hydrogen phosphate anions and ammonium cations in DAP with TiO2 and CsPbBr3 perovskite, respectively, but also ameliorates the interface contact and energy level alignment. Moreover, a higher quality perovskite film with fewer grain boundaries and defects is tightly formed on the DAP modified TiO2 layer arising from its lower wettability. Consequently, a substantially improved charge transport and extraction and minimized charge recombination are achieved in DAP tailored all-inorganic hole transport layer-free CsPbBr3 PSCs, yielding a power conversion efficiency as high as 10.31% with an impressive open-circuit voltage of 1.621 V, which is highly increased compared to 7.58% for the control device. Furthermore, the optimized device free of encapsulation exhibits a superior long-term stability after exposure to an air atmosphere at 85 °C with 85% RH over 720 h. [ABSTRACT FROM AUTHOR]

The passivation of defects at perovskite films, surfaces and the promotion of charge extraction across perovskite/carbon back interface are of vital importance to develop the power conversion efficiency (PCE) and stability of carbon‐based perovskite solar cells (PSCs) free of hole‐transporting layers (HTLs). Herein, an electron donor material with polyamino groups, hexamethylenetetramine (HMTA), is used as an efficient surface modifier for tribrominated all‐inorganic perovskite films. The modification with HMTA not only eliminates the defects by forming a bond between N atoms and positively charged ions but also optimizes the energy level structure of the perovskite film and back interface contact. Therefore, CsPbBr3 films with decreased trap states, extended carrier lifetimes, and enhanced hole mobility are gained, which significantly restrains charge recombination and energy loss as well as facilitates charge extraction and transfer at the perovskite/carbon interface. Finally, an improvement of PCE from 6.75% to 10.08% is obtained for carbon‐based HTL‐free CsPbBr3 PSCs without and with HMTA modification, respectively. Furthermore, the HMTA‐modified device without encapsulation presents an enhanced long‐term moisture and heat stability after being stored in the atmospheric environment with 80% relative humidity (RH) at 25 °C and 20% RH at 85 °C, respectively, due to the reduced defects and the improved hydrophobicity of perovskite film. [ABSTRACT FROM AUTHOR]