Aggregation of organic molecules plays a key role in determining the photoelectronic properties of various devices. However, the formation of aggregates is an outcome of complex synergistic effects of various intermolecular forces, and changes with the molecular structure and environment. Here we exploit the aggregation of two dyes with (MTPABT-Pyc) or without (MTPAcc) the nanosecond long-lived charge separation state and their effect on photovoltaic performance of dye-sensitized solar cells (DSSCs). Different solvent systems were selected to modulate the interactions between solvents and dye molecules for the effects on photophysical processes. Combining the experimental results on the solvent effect on dye aggregation with theoretical calculations reveals that MTPAcc inclines to form H-aggregation on the TiO2 surface because of the decisive role of its molecular structure. The solvent regulation has a great impact on MTPABT-Pyc which can make aggregates transform between H-aggregation and J-aggregation. The effects of aggregation on the device performance of two dyes are completely opposite. High performance of MTPAcc depends on the co-adsorbent chenodeoxycholic acid, which could suppress the dye aggregation. In contrast, the aggregation of MTPABT-Pyc will not harm the charge separation and transportation processes in devices and shows a positive effect on the cell performance due to the aggregation exhibiting broader absorption bands. As the photocurrent contribution by the aggregation-induced long-wavelength absorption increases from 9% (H-aggregation) to 34% (J-aggregation), the short-circuit current (Jsc) and the power conversion efficiency (PCE) of MTPABT-Pyc increased by 13% and 14%, respectively. These results pave a new way for taking full advantage of the aggregation of molecules to realize high-performance light-to-current conversion.