Polythiophene‐acid‐based conjugated polyelectrolytes have shown great potential as hole‐transport materials for the fabrication of inverted planar perovskite devices with decent power conversion efficiencies (PCEs), benefiting from their tunable structure and functional properties. In contrast to the current progress mainly from side functional group modification, here a simple and effective strategy is reported to effectively regulate the aggregation of P3CT‐K through the modification of the thiophene units in the main chain. A small molecule tris(pentafluorophenyl)borane (TPB) is applied as the Lewis acid to interact with the thiophene unit of polythiophene chain and regulate the aggregation of conjugated polyelectrolytes. The control of aggregation of P3CT‐K not only elevates the hole mobility of P3CT‐K, but also suppresses charge recombination in P3CT‐K composite films. Consequently, the high efficiency of inverted MAPbI3 perovskite solar cells is achieved with a peak power conversion efficiency of 20.7% and simultaneously improved short‐circuit current density and fill factor. This work provides an effective method for the aggregation control of the polyelectrolyte hole materials to promote the performance of inverted planar perovskite solar cells.