Improving the Fill Factor of Perovskite Solar Cells by Employing an Amine-tethered Diketopyrrolopyrrole-Based Polymer as the Dopant-free Hole Transport Layer

Although rapid progress has been witnessed recently in regular perovskite solar cells (PSCs), one of the bottlenecks to delay their industrialization is the complicated and poor reproducible doping process of the widely used hole-transporting material (HTM) Spiro-OMeTAD. To address this issue, herein, an unreported polymer, P25NH, has been synthesized and adopted as a dopant-free hole transport layer (HTL) in PSCs. Compared with the commonly used HTM poly(3-hexylthiophene), P25NH shows better aggregation property, enhanced ability of passivation to the perovskite surface, and higher mobility, which could greatly reduce series resistance and improve the fill factor. The PSCs with P25NH (1.6 mg/mL) as HTLs exhibited a decent power conversion efficiency (PCE) of 18.1% with a high fill factor of 81.9% (at 6 mg/mL, the fill factor is 83.2%). This work provides an alternative polymer for scalable dopant-free HTMs and a simple device structure for achieving high PCE.