Unveiling the Effect of Potassium Treatment on the Mesoporous TiO₂/ Perovskite Interface in Perovskite Solar Cells

Abstract

The morphological bulk defects and trap sites between TiO2 and the perovskite layer are critical issues in charge separation and electron transport. In this study, an effective method for improving the mesoporous TiO2/perovskite interfacial characteristics in perovskite solar cells (PSCs) is demonstrated by modifying mesoporous TiO2 with potassium (K) treatment. It is found that the modification of mesoporous TiO2 with the K treatment enhances the perovskite crystallization process, producing a perovskite film with higher crystallinity and larger grain sizes. It is also found that the K treatment not only effectively passivates the trap sites in mesoporous TiO2 but also reduces the sub-band-gap deep defect states at the interface of the perovskite, as revealed by photothermal deflection spectroscopy, thereby suppressing the nonradiative recombination and improving the V oc of the PSCs. Moreover, stronger photoluminescence quenching and shorter carrier lifetime are observed for the perovskite on K-treated mesoporous TiO2, indicating more efficient charge collection across the interface. As a result of these advancements, the PSC based on K-treated mesoporous TiO2 shows a high power conversion efficiency of 20.60% compared to the PSC without the K treatment (18.17%) and also significantly improves the environmental stability in ambient air.

Pushing the Limit of Open‐Circuit Voltage Deficit via Modifying Buried Interface in CsPbI3 Perovskite Solar Cells

“…And the Urbach Energy ( E u ), a measure for the degree of disorder within the material, could be fitted from the slope of the absorptance at the band edge. [ 30,31 ] The estimated E u for control TiO 2 and target TiO 2 is 279.2 and 211.3 meV, respectively, implying that SPA modification reduces the trap states density of TiO 2 . Hence, it confirms that the increased conductivity and electron mobility of target TiO 2 films can be attributed to improved film quality with inhibited oxygen vacancies and increased delocalized electrons obtained from oxygen atoms of SPA, suggesting that SPA‐modified TiO 2 films can be potentially used as high‐quality ETL for effective transport of photo‐generated electrons.…”

Recent Developments in Upscalable Printing Techniques for Perovskite Solar Cells

“…Thus, several research efforts have been made to fabricate low-temperature processed mesoporous PSCs and planar PSCs. [38][39][40][41] In addition, some other strategies such as interfacial engineering [42][43][44] and metal doping [45][46][47][48][49] have been employed to increase the PCE of the mesoporous PSCs. Similarly, for the conventional n-i-p structured mesoporous PSCs, SnO 2 scaffolds have been utilized as ETLs, which delivered a PCE of over 22%.…”

Combined Experimental and Simulation Studies of Lithium and Cobalt‐Modified TiO2 and Their Impacts on the Performance and Stability of Perovskite Solar Cells

“…Therefore, surface modification of TiO 2 has been widely studied and received much attention in academia. Despite the different methods recently proposed, posttreatment of TiO 2 has lately become a standard protocol for making reliable and efficient perovskite solar cells (PSCs), [2][3][4] which could be performed, for example, by using different metal-alkali salts, i.e., sodium (Na + ), potassium (K + ), lithium (Li + ), and cobalt (Co + ) ions, via thermal diffusion of their metal ions in either mesoscopic [5][6][7] or planar [8][9][10] -based device configurations. In principle, such doping should enhance the conductivity of the material due to the increasing electron/hole concentrations.…”

“…The introduction of (any) impurities modulates the optical properties of TiO 2 (i.e., the bandgap and structure (anatase or rutile)). While many reports show that the photovoltaic performance of perovskitebased devices was improved when a certain amount of such alkali salts was applied, [6,11] the role of such thermal treatment is not well understood. For instance, the K ion has an ionic radius of 1.33 Å [12] and is considered too large to be incorporated into the TiO 2 structure.…”