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Dopant‐free hole‐transporting layers (HTLs) are highly desired for realizing efficient and stable perovskite solar cells (PVSCs), but only very few of them can enable power conversion efficiencies (PCEs) over 20%. Herein, two imide‐functionalized triarylamine‐based donor‐acceptor (D‐A) type copolymers, PBTI‐TPA and PTTI‐TPA, are developed and applied as dopant‐free HTLs in inverted PVSCs. The combination of a classic redox‐active triphenylamine donor unit and an electron‐withdrawing oligothiophene imide co‐unit with rigid and planar backbone furnishes the two polymers with quasi‐planar backbone, suitable frontier molecular orbital (FMO) energy levels, favorable thermal stability, appropriate film morphology, and passivation effect. More importantly, the greatly improved hole mobility renders them as promising HTLs for PVSCs. As a result, the undoped PTTI‐TPA‐based inverted PVSCs deliver a remarkable PCE up to 21% as well as negligible hysteresis and substantial long‐term stability, outperforming the devices based on PBTI‐TPA and PTAA. The performance also represents one of the highest PCEs reported to date for PVSCs based on dopant‐free polymeric HTLs. The results highlight the great potentials of oligothiophene imides for constructing donor‐acceptor polymeric HTLs for enabling high‐performance dopant‐free PVSCs. [ABSTRACT FROM AUTHOR]

Hole transport materials (HTMs) are of great significance to improve the efficiency and long‐term stability of perovskite solar cells (PVSCs). Herein, a series of new HTMs based on isomeric dithienothiophene (DTT) are designed and synthesized. Effects of sulphur (S) atoms positions on defect passivation and performance of PVSCs are systematically investigated through theoretical computation, X‐ray diffraction, X‐ray photoelectron spectroscopy, etc. The three molecules display noticeable isomeric effect in energy level, light absorption, and hole mobility. With S atoms varied from bottom‐bottom‐bottom in 3T‐1 to bottom‐bottom‐top in 3T‐2, then to bottom‐top‐bottom in 3T‐3, the grown perovskite crystallite on the corresponding HTMs shows more homeogenous film morphology and less pinhole traps. Meanwhile, nonradiative recombination losses can be suppressed and hole extraction efficiency at HTM/perovskite surface can be improved from 3T‐1 to 3T‐3. As a result, the remarkable improvement of short‐circuit current density nd open‐circuit voltage in inverted perovskite solar cells can be realized with increasing the sulphur atoms contribution to the molecular conjugation. More importantly, 3T‐3‐based dopant‐free HTM achieves a top power conversion efficiency of 19.23% in PVSCs with good device stability under green solvent processing. These results demonstrate the role of S atoms positions in HTMs on photovoltaic performance of PVSCs and the potential of DTT in developing eco‐friendly HTMs toward efficient PVSCs. [ABSTRACT FROM AUTHOR]