We report the simplest possible method to date for fabricating robust, air-stable, sandwiched perovskite photodetectors. Unlike conventionally designed photodetectors, our proposed sandwiched structure does not require electron/hole transporting layers or expensive electrodes. We demonstrate that photocurrent and sensitivity are enhanced by an order of magnitude in the MAPbI3–MAPbBr3 heterojunction compared to the homojunctions of their analogues. This simpler approach may have applications in the perovskite-only class of solar cells with the goal of scaling up towards commercialization.