Zhiyuan Dai

In perovskite photovoltaics, self-assembled molecules (SAMs) have demonstrated the ability to enhance interface quality, reduce charge recombination, and improve energy-level alignment. However, most symmetrical molecules for photovoltaic applications tend to self-aggregate, which hinders uniform film formation, reduces the active surface area, and limits interface contact and device efficiency. In this work, we propose a symmetry-breaking co-assembly (SBC) strategy to improve the performance of the widely employed SAM of 2-[3,6-Dimethoxy-9H-carbazol-9-yl)ethyl] phosphonic acid (MeO-2PACz) by coupling with another small conjugated molecule, dibenzo[b,d]thiophene-4-carboxylic acid (DTCA). The broken symmetry at the molecular level enables the synthesis of co-SAM layers with significantly improved uniformity and coverage. A quantitative protocol based on atomic force microscope-infrared spectroscopy (AFM-IR) has been developed to determine the surface coverage of SAM layers. When the surface coverage of co-SAM layers is maximized, the interfacial chemical reaction under electrical stress and the non-radiative recombination loss are effectively suppressed, resulting in power conversion efficiencies (PCEs) of 26.32% (certified as 25.67%) and 25.34% for areas of 0.08 cm² and 1 cm², respectively. The encapsulated device retains 93% of its initial PCE after operating at the maximum power point (MPP) for 1,150 hours, as evaluated following the ISOS-L-1 protocol. These results underscore the effectiveness of the SBC strategy in advancing perovskite photovoltaics, and the coverage-maximizing methodology may be generalized to other research domains involving SAMs.

Low-dimensional conversion of lead iodide at perovskite grain boundaries (GBs) is of importance to address the interfacial instability of perovskite solar cells (PSCs), while current strategies relying on organic cations interacted with A/X site to low-dimensional lead-halide complexes are challenged by the instability caused by the introduction or residual cations and halides in perovskite films. Present work proposes and verifies a strategy of multidentate carbodithioate-lead chelation (MCLC), which is able to form a robust one-dimensional structure at the GBs, not only reducing interfacial defects and residual stress but also enhancing interfacial carrier transport in perovskite while substantially improving the photothermal and operational stabilities of PSCs. It was further demonstrated that bifacial modification at both top and buried interfaces of perovskite using MCLC strategy achieved PSCs with a high power conversion efficiency up to 26.15% (certified value of 25.75%) and 24.89% for 1-cm ² -area device. The device retains 90.1% of its initial efficiency after 1700 hours of maximum power point tracking under illumination.