Shaobing Xiong

Abstract Ternary architecture is a promising strategy to enhance power conversion efficiencies (PCEs) of organic solar cells (OSCs). However, among all the photovoltaic parameters that govern the final PCEs, the fill factor (FF) for ternary OSCs is generally below 78%, limiting solar cells’ performance. Here, charge dynamics in the ternary cells PM6:DRTB‐T‐C4:Y6 with a FF of 80.88% and a PCE of 17.05% are thoroughly investigated by a series of transient characterization technologies, including transient absorption spectroscopy, transient photovoltage, and transient photocurrent measurements. The impressive FF results from effective exciton dissociation, enhanced charge transport and suppressed recombination in ternary cells. Moreover, the correlation between the measured FF and the charge recombination‐extraction competition is quantitatively analyzed by using a circuit model. The ternary cells also show small energy loss ( E loss ). The findings here provide insight into achieving high‐FF and low‐ E loss ternary OSCs.

Abstract 2D Ruddlesden–Popper perovskites (RPPs) are emerging as potential challengers to their 3D counterpart due to superior stability and competitive efficiency. However, the fundamental questions on energetics of the 2D RPPs are not well understood. Here, the energetics at (PEA) 2 (MA) n −1 Pb n I 3 n +1 /[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) interfaces with varying n values of 1, 3, 5, 40, and ∞ are systematically investigated. It is found that n–n junctions form at the 2D RPP interfaces ( n = 3, 5, and 40), instead of p–n junctions in the pure 2D and 3D scenarios ( n = 1 and ∞). The potential gradient across phenethylammonium iodide ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, reducing charge recombination, which contributes to the smallest energy loss and the highest open‐circuit voltage ( V oc ) in the perovskite solar cells (PSCs) based on the 2D RPP ( n = 5)/PCBM. The mechanism is further verified by inserting a thin 2D RPP capping layer between pure 3D perovskite and PCBM in PSCs, causing the V oc to evidently increase by 94 mV. Capacitance–voltage measurements with Mott–Schottky analysis demonstrate that such V oc improvement is attributed to the enhanced potential at the interface.