Thermally Modulated Quartz Crystal Microbalance for Multimolecular Adsorption Decoupling: A Selective Desorption Strategy for Precision Interface Engineering

In dye-sensitized solar cells (DSCs), while increasing dye loading (e.g., with N719) enhances light absorption, excessive loading induces molecular aggregation, which consequently compromises device performance. The introduction of coadsorbents such as chenodeoxycholic acid (CDCA) effectively suppresses this aggregation; however, competitive adsorption between coadsorbents and dye molecules carries the risk of insufficient dye loading. Achieving an optimal balance between coadsorbent and dye concentrations requires precise quantification of their respective surface masses. Unfortunately, no simple method currently exists to directly determine the individual molecular masses within the mixed adsorption layer on TiO2 surfaces. To address these challenges, this study employed temperature-modulated quartz crystal microbalance (QCM) technology, which revealed a novel characteristic of significant thermal stability differences between the N719 dye and CDCA molecules on the TiO2 surface. Building on this finding, we developed a thermally selective quantitative detection approach that enables the direct quantification of N719 and CDCA adsorption on the TiO2 surface. This study has also innovatively transformed the detrimental high-temperature desorption of CDCA into an advantageous opportunity for interface engineering, establishing a novel adsorption site thermal maneuver supplementary sensitization (ASTM-SS) strategy. The sensitization process is accomplished through three consecutive steps, including CDCA-directed assembly of ordered dye monolayers, thermally selective CDCA removal for active site regeneration, and supplementary sensitization to achieve optimal surface coverage. This approach enhances the N719 loading on TiO2 by 126.7%, while photovoltaic tests demonstrate a 156.3% improvement in short-circuit current density (Jsc) and a corresponding enhancement in power conversion efficiency. Our work not only provides an innovative approach for the analysis of coadsorption systems but also introduces a new paradigm for solar cell interface engineering, offering critical guidance for the development of efficient and stable devices. Furthermore, this strategy demonstrates broad universality and holds potential application value in other multimolecular adsorption systems.