Polarized Molecule 4-(Aminomethyl) Benzonitrile Hydrochloride for Efficient and Stable Perovskite Solar Cells

PTAA-Based Perovskite Photovoltaics Catching up: Ionic Liquid Engineering-Assisted Crystallization Through Sequential Deposition

PTAA as a widely studied polymeric hole transporting material, has garnered significant attention due to its outstanding thermal and chemical stability. However, the performance of PTAA-based p-i-n devices is shown to lag behind counterpart utilizing oxides or SAMs. In this study, the ionic liquid, 1-ethyl-3-methylimidazolium formate (EMIMCOOH), is innovatively introduced into the lead iodide (PbI2) precursor solution, resulting in a more pronounced mesoporous PbI2 film with expended pore-size and denser pores. This enhancement is attributed to the coordination bond between the ─C═O group in EMIMCOOH and Pb2+. This intensified mesoporous morphology not only facilities the reaction between PbI2 and the organic layer, but also promotes the PbI2 conversion into perovskite material. Importantly, the incorporation of EMIMCOOH slows down the perovskite conversion process, increasing perovskite domain size and suppressed Pb0 trap density, resulting in a uniform perovskite layer with enhanced charge transport properties, as evidenced by the conducting atomic force microscope (c-AFM) results. As a result, the incorporation of EMIMCOOH yields a power conversion efficiency (PCE) of 24.10% and a high fill factor exceeding 85%. Notably, the PCE of the EMIMCOOH-modified device can still maintain 86% of the initial value after 1500 h at 25 °C in an N2 atmosphere.

A Multifunctional Dye Molecule as the Interfacial Layer for Perovskite Solar Cells

In perovskite solar cells (PSCs), defects in the interface and mismatched energy levels can damage the device performance. Improving the interface quality is an effective way to achieve efficient and stable PSCs. In this work, a multifunctional dye molecule, named ThPCyAc, was designed and synthesized to be introduced in the perovskite/HTM interface. On one hand, various functional groups on the acceptor unit can act as Lewis base to reduce defect density and suppress nonradiative combinations. On the other hand, the stepwise energy-level alignment caused by ThPCyAc decreases the accumulation of interface carriers for facilitating charge extraction and transmission. Therefore, based on the ThPCyAc molecule, the devices exhibit elevated open-circuit voltage and fill factor, resulting in the best power conversion efficiency (PCE) of 23.16%, outperforming the control sample lacking the interface layer (PCE = 21.49%). Excitingly, when attempting to apply it as a self-assembled layer in inverted devices, ThPCyAc still exhibits attractive behavior. It is worth noting that these results indicate that dye molecules have great potential in developing multifunctional interface materials to obtain higher-performance PSCs.

The synergistic effect of trap deactivation and hysteresis suppression at grain boundaries in perovskite interfaces via multifunctional groups

In spite of the outstanding photoelectric properties of perovskite materials, numerous defects produced in the preparation process eventually result in decomposition of the perovskite layer. To date, the mechanism of defect passivation and hysteresis reduction via additive engineering has still been obscure for perovskite materials, which seriously restricts performance improvement of the devices. Herein, conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) measurements were applied to probe carbamic acid ethyl ester (EU)-based trap passivation and suppression of hysteresis in perovskite films. The results indicate that the internal interaction between multifunctional bonds ("CO" and "-NH2") of EU and Pb2+ ions of the perovskite may inactivate the trap state and inhibit ion migration within sub-grains and grain boundaries (GBs), resulting in improvement of the long-term stability of the cells. In consequence, the EU-modified champion device prepared in all-air achieved a power conversion efficiency (PCE) of 20.10%, one of the high performances for the devices fabricated in air to date. In short, this work will propose some interesting speculation about ion migration as well as its influence on hysteresis in perovskite materials.