Tailoring the Molecular Structure of Dopant-Free Polymeric Hole Transport Materials for Improved Charge Extraction in Perovskite Quantum Dot Solar Cells

We have developed three dopant-free hole transport materials (HTMs) as an alternative to the commonly used doped Spiro-OMeTAD in perovskite quantum dot solar cells (PQD-SCs). The dominant HTM, Spiro-OMeTAD, requires the use of doping systems to enhance charge mobility. However, these dopants can lead to the degradation of PQD-SCs, making the development of efficient dopant-free HTMs crucial for commercialization. In our study, we designed three types of dopant-free HTMs: Asy-PDTS, Asy-PSDTS, and Asy-PSeDTS. To improve their electrical properties, we incorporated a chalcogenide-based fluorinated benzothiadiazole rigid segment acceptor unit. This rigid segment acted as an effective charge hopping channel, compensating for the impaired electrical properties through side chain engineering. Through a conformation-locking approach utilizing chalcogenide-fluorine noncovalent interactions, we achieved favorable planar structures with face-to-face stacking of the rigid segments. Among the optimized devices, the one utilizing Asy-PSeDTS exhibited remarkable performance. It achieved a power conversion efficiency (PCE) of 15.2%, the highest reported PCE among dopant-free HTM-based PQD-SCs. Additionally, this device maintained 80% of its initial PCE even after 40 days, demonstrating superior stability compared to other dopant-free HTM-based PQD-SCs.