Simultaneous Enhanced Efficiency and Stability of Perovskite Solar Cells Using Adhesive Fluorinated Polymer Interfacial Material

Fluorinated Polyimide Tunneling Layer for Efficient and Stable Perovskite Photovoltaics

Despite the remarkable progress of perovskite solar cells (PSCs), challenges remain in terms of finding effective and viable strategies to enhance their long-term stability while maintaining high efficiency. In this study, a new insulating and hydrophobic fluorinated polyimide (FPI: 6FDA-6FAPB) was used as the interface layer between the perovskite layer and the hole transport layer (HTL) in PSCs. The functional groups of FPI play a pivotal role in passivating interface defects within the device. Due to its high work function, FPI demonstrates field-effect passivation (FEP) capabilities as an interface layer, effectively mitigating non-radiative recombination at the interface. Notably, the FPI insulating interface layer does not impede carrier transmission at the interface, which is attributed to the presence of hole tunneling effects. The optimized PSCs achieve an outstanding power conversion efficiency (PCE) of 24.61 % and demonstrate excellent stability, showcasing the efficacy of FPI in enhancing device performance and reliability.

Simultaneous Enhancement of Efficiency and Operational-Stability of Mesoscopic Perovskite Solar Cells via Interfacial Toughening

The combined effects of compact TiO2 (c-TiO2 ) electron-transport layer (ETL) are investigated without and with mesoscopic TiO2 (m-TiO2 ) on top, and without and with an iodine-terminated silane self-assembled monolayer (SAM), on the mechanical behavior, opto-electronic properties, photovoltaic (PV) performance, and operational-stability of solar cells based on metal-halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c-TiO2 without SAM to m-TiO2 with SAM. This is attributed to the synergistic effect of the m-TiO2 /MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine-terminated silane SAM. The combination of m-TiO2 and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power-conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1 cm2 active areas, respectively. These PSCs also have exceptionally long operational-stability lives: extrapolated T80 (duration at 80% initial PCE retained) is ≈18 000 and 10 000 h for 0.1 and 1 cm2 active areas, respectively. Postmortem characterization and analyses of the operational-stability-tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational-stability.

Controlling Molecular Orientation of Small Molecular Dopant-Free Hole-Transport Materials: Toward Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have great potential for future application. However, the commercialization of PSCs is limited by the prohibitively expensive and doped hole-transport materials (HTMs). In this regard, small molecular dopant-free HTMs are promising alternatives because of their low cost and high efficiency. However, these HTMs still have a lot of space for making further progress in both efficiency and stability. This review firstly provides outlining analyses about the important roles of molecular orientation when further enhancements in device efficiency and stability are concerned. Then, currently studied strategies to control molecular orientation in small molecular HTMs are presented. Finally, we propose an outlook aiming to obtain optimized molecular orientation in a cost-effective way.

Bifunctional Cellulose Interlayer Enabled Efficient Perovskite Solar Cells with Simultaneously Enhanced Efficiency and Stability

Interfacial engineering is a vital strategy to enable high-performance perovskite solar cells (PSCs). To develop efficient, low-cost, and green biomass interfacial materials, here, a bifunctional cellulose derivative is presented, 6-O-[4-(9H-carbazol-9-yl)butyl]-2,3-di-O-methyl cellulose (C-Cz), with numerous methoxy groups on the backbone and redox-active carbazole units as side chains. The bifunctional C-Cz shows excellent energy level alignment, good thermal stability and strong interactions with the perovskite surface, all of which are critical for not only carrier transportation but also potential defects passivation. Consequently, with C-Cz as the interfacial modifier, the PSCs achieve a remarkably enhanced power conversion efficiency (PCE) of 23.02%, along with significantly enhanced long-term stability. These results underscore the advantages of bifunctional cellulose materials as interfacial layers with effective charge transport properties and strong passivation capability for efficient and stable PSCs.

Synergistic Effects of Interfacial Energy Level Regulation and Stress Relaxation via a Buried Interface for Highly Efficient Perovskite Solar Cells

An electron-transport layer with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). In addition, interface stress and lattice distortion are inevitable during the crystallization process of perovskite. Herein, IT-4F is introduced into PSCs at the buried SnO₂ and perovskite interface, which assists in releasing the residual stress in the perovskite layer. Meanwhile, the work function of SnO₂/IT-4F is lower than that of SnO₂, which facilitates charge transfer from perovskite to ETL and consequently leads to a significant improvement in the power conversion efficiency (PCE) to 23.73%. The V_OC obtained is as high as 1.17 V, corresponding to a low voltage deficit of 0.38 V for a 1.55 eV bandgap. Consequently, the device based on IT-4F maintains 94% of the initial PCE over 2700 h when stored in N₂ and retains 87% of the initial PCE after operation for 1000 h.

Novel Push-Pull Benzodithiophene-Containing Polymers as Hole-Transport Materials for Efficient Perovskite Solar Cells

Donor-acceptor conjugated polymers are considered advanced semiconductor materials for the development of thin-film electronics. One of the most attractive families of polymeric semiconductors in terms of photovoltaic applications are benzodithiophene-based polymers owing to their highly tunable electronic and physicochemical properties, and readily scalable production. In this work, we report the synthesis of three novel push-pull benzodithiophene-based polymers with different side chains and their investigation as hole transport materials (HTM) in perovskite solar cells (PSCs). It is shown that polymer P3 that contains triisopropylsilyl side groups exhibits better film-forming ability that, along with high hole mobilities, results in increased characteristics of PSCs. Encouraging a power conversion efficiency (PCE) of 17.4% was achieved for P3-based PSCs that outperformed the efficiency of devices based on P1, P2, and benchmark PTAA polymer. These findings feature the great potential of benzodithiophene-based conjugated polymers as dopant-free HTMs for the fabrication of efficient perovskite solar cells.

Effects of polyethylene oxide particles on the photo-physical properties and stability of FA-rich perovskite solar cells

In this paper, we use Polyethylene Oxide (PEO) particles to control the morphology of Formamidinium (FA)-rich perovskite films and achieve large grains with improved optoelectronic properties. Consequently, a planar perovskite solar cell (PSC) is fabricated with additions of 5 wt% of PEO, and the highest PCE of 18.03% was obtained. This solar cell is also shown to retain up to 80% of its initial PCE after about 140 h of storage under the ambient conditions (average relative humidity of 62.5 ± 3.25%) in an unencapsulated state. Furthermore, the steady-state PCE of the PEO-modified PSC device remained stable for long (over 2500 s) under continuous illumination. This addition of PEO particles is shown to enable the tuning of the optoelectronic properties of perovskite films, improvements in the overall photophysical properties of PSCs, and an increase in resistance to the degradation of PSCs.

Multifunctional π-Conjugated Additives for Halide Perovskite

Additive is a conventional way to enhance halide perovskite active layer performance in multiaspects. Among them, π-conjugated molecules have significantly special influence on halide perovskite due to the superior electrical conductivity, rigidity property, and good planarity of π-electrons. In particular, π-conjugated additives usually have stronger interaction with halide perovskites. Therefore, they help with higher charge mobility and longer device lifetime compared with alkyl-based molecules. In this review, the detailed effect of conjugated molecules is discussed in the following parts: defect passivation, lattice orientation guidance, crystallization assistance, energy level rearrangement, and stability improvement. Meanwhile, the roles of conjugated ligands played in low-dimensional perovskite devices are summarized. This review gives an in-depth discussion about how conjugated molecules interact with halide perovskites, which may help understand the improved performance mechanism of perovskite device with π-conjugated additives. It is expected that π-conjugated organic additives for halide perovskites can provide unprecedented opportunities for the future improvement of perovskite devices.