The efficiency of organic solar cells has raised drastically in the past years. However, there is an undeniable lack of hole transport layers that can provide high carrier selectivity, low defect density, and high processing robustness, simultaneously. In this work, this issue is addressed by studying defect generation and surface passivation of nickel oxide (NiOx). It is revealed that the generation of high oxidation state species on NiOx surface lowers contact resistance but hinders charge extraction when employed as transport layer in organic solar cells. By using them as coordination centers, a straightforward surface modification strategy is implemented using (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) that enhances charge extraction and increases the solar cell efficiency from 11.46% to 17.12%. Additionally, the robustness of this modification across different deposition methods of the carbazole molecule is demonstrated. Finally, by fine-tuning the Fermi level using various carbazole-based molecules, and in particular with ((4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (4PADCB), a power conversion efficiency of 17.29% is achieved, with an outstanding combination of a VOC of 0.888 V and a fill factor of 80%.

Recently, carbazole‐based self‐assembled monolayers (SAMs) have been utilized as hole transport layers (HTLs) in perovskite solar cells. However, their application in Sn or mixed Sn/Pb perovskite solar cells has been hindered by the poor wettability of the perovskite precursor solution on the carbazole surface. Here a self‐assembled bilayer (SAB) comprising a covalent monolayer (Br‐2PACz) and a noncovalent wetting layer (4CzNH 3 I) as the HTL in a Cs 0.25 FA 0.75 Sn 0.5 Pb 0.5 I 3 perovskite solar cell is proposed. It is demonstrated that the wetting layer completely solves the problem due to the higher polarity of the surface and, furthermore, the ammonium groups help in the passivation of trap states at the buried SAB/perovskite interface. The introduction of the SAB enhances the device reproducibility with an average efficiency of 18.98 ± 0.28% (19.45% for the best device), compared to 11.54 ± 9.36% (19.34% for the best device) for the SAM‐only devices. Furthermore, the improved perovskite processability on the SAB helps to increase the reproducibility of larger size device, where, a 12.5% efficiency for a 0.8 cm 2 active area device compared to 0.68% for the best SAM‐based solar cell is demonstrated. Finally, the device's operational stability is also improved to 358 hours (T 80% ), compared to 220 hours for the SAM‐based solar cell.

Hybrid perovskite solar cells have attracted an unprecedented research attention due to their skyrocketing record power conversion efficiency (PCE), which now exceeds 23% in less than a decade from the initial PCE of 3.8%. Besides the excellent optoelectronic properties of the perovskite absorbers, the high efficiencies are also dependent on preparation methods and advanced device engineering. In this study, the role of the device architecture (planar n‐i‐p vs inverted p‐i‐n structure) and of the charge‐selective interlayer on the photophysical properties of the perovskite absorber and device performance are explored. FA 0.85 MA 0.15 PbBr 0.45 I 2.55 (MA = methylammonium, FA = formamidinium) as the perovskite absorber and chloride‐capped TiO 2 colloidal nanocrystals (TiO 2 ‐Cl) and poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as close‐to‐the‐substrate layers in the conventional and inverted structures are employed, respectively. Extremely different device performances are demonstrated by the two structures. The device where the active layer is deposited on TiO 2 ‐Cl displays a champion PCE of 19.9%, while the one using PEDOT:PSS gives about 15.1% efficiency. The photophysical and electrical investigations indicate that the TiO 2 ‐Cl/perovskite interface has lower number of traps, underlining the importance of interfaces for achieving highly performing perovskite solar cells.