The key for fabricating efficient organic/n‐Si planar heterojunction solar cells is the organic semiconductor layer, which governs key steps in photocarrier harvesting such as charge carrier separation and extraction. Typical organic semiconductors, however, are inadequate to yield good device performance due to their low electrical conductivities and undesirable work functions. Herein, a method is proposed to boost charge carrier concentration in poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) from 1018 to 1022 cm−3 by combining solvent p‐doping and DMF treatment. This high carrier concentration induces significant band bending in the Si substrate and thus leads to an extended inversion zone near an organic/Si heterojunction. It is found that this type of heterojunction creates a broad built‐in electric field and effective interface passivation. The highly conductive PEDOT:PSS enables a simple and efficient organic/n‐Si planar heterojunction solar cell with a power conversion efficiency exceeding 13% without using complex light‐trapping structures. This power efficiency is comparable with the highest value reported to date. Herein, the possibility of making effective organic/n‐Si planar heterojunction solar cells simply by applying a layer of extremely conductive organic coating is demonstrated.

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