Interfacial positioning of LiI-doped PEDOT:PSS in homojunction bilayer towards hole extraction and perovskite growth for solar cells

Organic semiconductors have been widely explored with additive and interface engineering to find their novel properties and applications for solid-state devices. In this work, conductive polymer PEDOT:PSS was doped with lithium iodide (LiI) via solution processing to induce the PEDOT separation from PSS phase and PEDOT linear conformation. With this restructuring, LiI-doped PEDOT:PSS film exhibits a higher electrical conductivity and lower work function, and its surface becomes smoother and less hydrophilic. Herein, we developed a homojunction bilayer by stacking LiI-doped PEDOT:PSS and pristine PEDOT:PSS via spin-coating and annealing processes, and elucidated an interfacial coupling strategy via inter-PEDOT crystallization to tailor the textural coherence and electrical enhancement of the compatible bilayer. This bilayer surface benefits the growth of superior perovskite (MAPbI 3 ) film under ambient medium-humidity and low-oxygen conditions, and offers an excellent capability for the hole extraction from adjacent perovskite. A dependence of the carrier dynamics on the perovskite crystallinity and PEDOT:PSS conductivity is suggested. In a simple inverted perovskite solar cell (PSC) without encapsulation, the homojunction bilayer facilitates charge-carrier separation and suppresses recombination to promote photocurrent with negligible hysteresis, attaining a marked enhancement by 22.8 % in the power conversion efficiency surpassing the pristine single-layer. This study paves the way for a full exploration of the PEDOT:PSS morphology and conductivity in the transport bilayer design towards further advancement of optoelectronic devices. • LiI doping in PEDOT:PSS film favors electrical conductivity and smooth surface. • Interfacial coupling strategy tailors textural coherence and electrical enhancement. • Compatible PEDOT:PSS bilayer benefits perovskite growth and rapid hole extraction. • Homojunction bilayer promotes charge collection and photocurrent yield.