Here, taking layered polymeric carbon nitride (CN) as an example, the dominant role of in-plane charge transport is demonstrated both theoretically and experimentally. The in-plane "sewing" and interlayer "cutting" effects of three alkaline potassium salts on the CN polymerization process are enhanced with the increase of alkalinity. The in-plane crystallinity-dependent charge transfer and separation and photocatalytic activity are elucidated through the samples of three alkaline potassium salt series. Our findings provide guidance for improving the photoelectric conversion efficiency by optimizing in-plane charge transfer rather than interlayer charge transfer, targeting layered photoelectric conversion materials.