Suppressing nonradiative recombination at the interface between the organometal halide perovskite (PVK) and the charge‐transport layer (CTL) is crucial for improving the efficiency and stability of PVK‐based solar cells (PSCs). Here, a new bathocuproine (BCP)‐based nonconjugated polyelectrolyte (poly‐BCP) is synthesized and this is introduced as a “dual‐side passivation layer” between the tin oxide (SnO2) CTL and the PVK absorber. Poly‐BCP significantly suppresses both bulk and interfacial nonradiative recombination by passivating oxygen‐vacancy defects from the SnO2 side and simultaneously scavenges ionic defects from the other (PVK) side. Therefore, PSCs with poly‐BCP exhibits a high power conversion efficiency (PCE) of 24.4% and a high open‐circuit voltage of 1.21 V with a reduced voltage loss (PVK bandgap of 1.56 eV). The non‐encapsulated PSCs also show excellent long‐term stability by retaining 93% of the initial PCE after 700 h under continuous 1‐sun irradiation in nitrogen atmosphere conditions.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been one of the most established hole transport layers (HTL) in organic solar cells (OSCs) for several decades. However, the presence of PSS − ions is known to deteriorate device performance via a number of mechanisms including diffusion to the HTL-active layer interface and unwanted local chemical reactions. In this study, it is shown that PSS − ions can also result in local p-doping in the high efficiency donor:non-fullerene acceptor blendsresulting in photocurrent loss. To address these issues, a facile and effective approach is reported to improve the OSC performance through a two-component hole transport layer (HTL) consisting of a self-assembled monolayer of 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) and PEDOT:PSS. The power conversion efficiency (PCE) of 17.1% using devices with PEDOT:PSS HTL improved to 17.7% when the PEDOT:PSS/2PACz two-component HTL is used. The improved performance is attributed to the overlaid 2PACz layer preventing the formation of an intermixed p-doped PSS − ion rich region (≈5-10 nm) at the bulk heterojunction-HTL contact interface, resulting in decreased recombination losses and improved stability. Moreover, the 2PACz monolayer is also found to reduce electrical shunts that ultimately yield improved performance in large area devices with PCE enhanced from 12.3% to 13.3% in 1 cm 2 cells.

The highest-efficiency organic photovoltaic (OPV)-based solar cells, made from blends of electron-donating and electron-accepting organic semiconductors, are often characterized by strongly reduced (non-Langevin) bimolecular recombination. Although the origins of the reduced recombination are debated, mechanisms related to the charge-transfer (CT) state and free-carrier encounter dynamics controlled by the size of donor and acceptor domains are proposed as underlying factors. Here, a novel photoluminescence-based probe is reported to accurately quantify the donor-acceptor domain size in OPV blends. Specifically, the domain size is measured in high-efficiency non-fullerene acceptor (NFA) systems and a comparative conventional fullerene system. It is found that the NFA-based blends form larger domains but that the expected reductions in bimolecular recombination attributed to the enhanced domain sizes are too small to account for the observed reduction factors. Further, it is shown that the reduction of bimolecular recombination is correlated to enhanced exciton dynamics within the NFA domains. This indicates that the processes responsible for efficient exciton transport also enable strongly non-Langevin recombination in high-efficiency NFA-based solar cells with low-energy offsets.