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Perovskite solar cells (PSCs) have achieved a certified power conversion efficiency (PCE) of 25.5% and show potential for low‐cost photovoltaic applications. One key of pushing PSCs into industrialization is enlarging their areas. However, the PCE of larger‐area PSCs is dramatically limited by the undesired increase in series resistance (RS), which leads to obvious loss of fill factor (FF). Herein, RS in fully printable mesoscopic PSCs is modulated with a carbon electrode by optimizing the device geometry, preparing busbars to collect currents from electrodes and improving the conductivity of the back electrode. A rectangular device shape and tin busbars on conductive substrate effectively reduce the RS. Meanwhile, an additional hot‐pressed highly conductive low‐temperature carbon layer on the back carbon electrode also reduces the RS. An enhanced PCE of 13.99% for 1 cm2 PSCs by RS modulation is obtained, whereas the control device exhibits a PCE of 7.74%. The PCE increase is due to the improvement of FF from 0.372 to 0.638 with reduced RS from 27.13 to 9.66 Ω cm2. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are considered to be the most promising next‐generation photovoltaic technology. Among all the configurations of PSCs, the printable hole‐conductor‐free mesoscopic PSC (p‐MPSC) has unique advantages on low cost, large‐area fabrication and fabulous stability, which endows it with the greatest potential for industrialization. The interfacial recombination losses, especially at the perovskite/carbon interface, are the bottleneck for further improving the power conversion efficiency (PCE) of p‐MPSCs. 2‐Bromo‐6‐fluoronaphthalene is introduced as an interfacial modulator for p‐MPSCs through post‐treatment. The bromo‐terminal acts as an electrophilic site to interact with the iodine ion in perovskite via the noncovalent halogen bond. Meanwhile, the fused ring of naphthalene is capable to accommodate electron density that is attracted from the perovskite. This interaction induces a more favorable band structure at the interface. The hole extraction is promoted and the interfacial nonradiative recombination is inhibited. Accordingly, a champion p‐MPSC with an improved PCE of 16.77% from 15.50% of the pristine device is obtained. [ABSTRACT FROM AUTHOR]