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[Display omitted] • An efficient PPPDE interlayer is inserted for the first time in the ETL-free PSCs. • The champion device yields an extraordinary PCE of up to 19.71%. • Ameliorated hysteresis and stability are achieved in PPPDE-based ETL-free PSCs. Organic-inorganic halide perovskites have become promising materials for the next generation of photovoltaic devices on account of the preeminent optoelectronic characteristics and boundless potentialities. Perovskite solar cells (PSCs) normally require a complex structure design with an electron transport layer (ETL) to provide a built-in electric field and depress the probability of carrier recombination. Nonetheless, the construction of a proper ETL is not cost-effective, which precludes the practical commercialization of the PSCs. In this respect, a simplified ETL-free PSC is successfully fabricated by inserting a facile and efficient 1-[N-(2-Hydroxyethyl)-4′-piperidyl]-3-(4′-piperidyl) propane (PPPDE) small-molecule thin interlayer between the FTO substrate and perovskite film. Compared with the bare FTO-based PSCs, this surface engineering can prominently ameliorate the photovoltaic performance parameters, yielding an extraordinary PCE of up to 19.71% with a ca. 31% efficiency enhancement, which can be attributed to the optimized interface energy-level alignment with a barrier-free contact, the elevated charge transfer and collection as well as the suppressed electron-holes recombination at the FTO/perovskite interface. Synchronously, the long-term air stability is also improved with mitigated J – V hysteretic behavior due to the larger grain size of perovskite and the suppressed defect-induced degradation. Furthermore, an augmented performance of 15.87% was achieved for the flexible PPPDE embedded ETL-free PSC fabricated on ITO/PEN substrates via a low-temperature deposition process. The demonstrated PPPDE interlayer presents a brand-new strategy that can simplify the cell configuration and improve the photovoltaic performance of ETL-free PSCs. [ABSTRACT FROM AUTHOR]

• Ag substitution greatly improves the performance of CuSbS 2 solar cells. • Single phase Ag-substituted CuSbS 2 film is achieved by spray pyrolysis. • Ag substitution could inhibit Sb 2 S 3 impurities. • The device shows a really stable performance in damp-heating condition. CuSbS 2 has been considered as a promising photovoltaic absorber material, due to its earth abundant and environmentally friendly constituents. However, the electron affinity and similar radius of cations bring heavy atomic disorders in CuSbS 2 film, limiting its photovoltaic performance. Herein, we report an efficient way to reduce disorders by introducing Ag atom into CuSbS 2 crystal structure. The crystal structure and chemical analysis confirm that Ag occupies the Cu position in the as-prepared films by the spray pyrolysis. The absorption spectra combined with photoluminescence measurement indicate that Ag-substituted CuSbS 2 films have fewer recombination centers. The density functional theory calculation result reveals that Ag-substituted CuSbS 2 has a more stable crystal structure, and the formation energy of the primary point defects obviously increases. Therefore, Ag-substituted CuSbS 2 photovoltaic device shows asignificantly improved power conversion efficiency from 0.73% to 2.48%. [ABSTRACT FROM AUTHOR]