Tailoring the Dimensionality of Hybrid Perovskites in Mesoporous Carbon Electrodes for Type‐II Band Alignment and Enhanced Performance of Printable Hole‐Conductor‐Free Perovskite Solar Cells

Printable hole‐conductor‐free perovskite solar cells (PSCs) have attracted intensive research attention due to their high stability and simple manufacturing process. However, the cells have suffered severe potential loss in the absence of the hole transporting layer. The dimensionality of the perovskite absorber in the mesoporous carbon electrodes by conducting post‐treatments is reduced. The low‐dimensional perovskites possess wide‐bandgaps and form type‐II band alignment, favoring directional charge transportation and thus enhancing the device performance. For the cells using MAPbI 3 (MA = methylammonium) as the light absorber, the open‐circuit voltage ( V OC ) is significantly enhanced from 0.92 to 0.98 V after posttreatment, delivering an overall efficiency of 16.24%. For the cells based on FAPbI 3 (FA = formamadinium), a high efficiency of 17.47% is achieved with V OC of 1.02 V, which are both the highest reported values for printable hole‐conductor‐free PSCs. This strategy provides a facile method for tuning the energy level alignment for mesoscopic perovskite‐based optoelectronics.