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Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized π-conjugated structures, hole extraction is expected to be more efficient when the π-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration. The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 23.0%.

High-performance and cost-effective hole-collecting materials (HCMs) are indispensable for commercially viable perovskite solar cells (PSCs). Here, we report an anchorable HCM composed of a triazatruxene core connected with three alkyl carboxylic acid groups (3CATAT-C3). In contrast to the phosphonic acid-containing tripodal analog (3PATAT-C3), 3CATAT-C3molecules can form a hydrophilic monolayer on a transparent conducting oxide surface, which is beneficial for subsequent perovskite film deposition in the traditional layer-by-layer fabrication process. More importantly, the larger diffusion coefficient and higher surface energy make 3CATAT-C3suitable for the simplified, cost-effective one-step co-deposition process in which 3CATAT-C3was directly added as part of the perovskite precursor solution. 3CATAT-C3is predominantly located at the perovskite bottom surface after spin-coating the mixed precursor solution, facilitating charge extraction. Devices with 3CATAT-C3fabricated by this co-deposition method exhibit superior performance with a champion power conversion efficiency of over 23%. The unencapsulated devices showed good operational stability (retaining 90% of the initial output after 100 h), thermal durability (retaining 95% of the initial value after heating at 105 °C under air), and excellent storage stability (showing no drop in performance over 8000 h). Based on the results of time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) and diffusion order nuclear magnetic resonance spectroscopy (DOSY), we elucidated the effect of anchoring groups on the performance of the tripodal HCMs in PSCs as well as the mechanism of the co-deposition fabrication process. Our findings provide valuable insights for the molecular design of multifunctional hole-collecting materials, further advancing the performance of perovskite solar cells.

Perovskite interfaces critically influence the final performance of the photovoltaic devices. Optimizing them by reducing the defect densities or improving the contact with the charge transporting material is key to further enhance the efficiency and stability of perovskite solar cells. Inverted (p–i–n) devices can particularly benefit here, as evident from various successful attempts. However, every reported strategy is adapted to specific cell structures and compositions, affecting their robustness and applicability by other researchers. In this work, we present the universality of perovskite top surface post-treatment with ethylenediammonium diiodide (EDAI2) for p–i–n devices. To prove it, we compare devices bearing perovskite films of different composition, i.e., Sn-, Pb-, and mixed Sn–Pb-based devices, achieving efficiencies of up to 11.4, 22.0, and 22.9%, respectively. A careful optimization of the EDAI2thickness indicates a different tolerance for Pb- and Sn-based devices. The main benefit of this treatment is evident in the open-circuit voltage, with enhancements of up to 200 mV for some compositions. In addition, we prove that this treatment can be successfully applied by both wet (spin-coating) and dry (thermal evaporation) methods, regardless of the composition. The versatility of this treatment makes it highly appealing for industrial application, as it can be easily adapted to specific processing requirements. We present a detailed experimental protocol, aiming to provide the community with an easy, universal perovskite post-treatment method for reliably improving the device efficiency, highlighting the potential of interfaces for the field.