Crosslinkable and Chelatable Organic Ligand Enables Interfaces and Grains Collaborative Passivation for Efficient and Stable Perovskite Solar Cells

Interface Reactive Sputtering of Transparent Electrode for High-Performance Monolithic and Stacked Perovskite Tandem Solar Cells

Sputtered indium tin oxide (ITO) fulfills the requirements of top transparent electrodes (TTEs) in semitransparent perovskite solar cells (PSCs) and stacked tandem solar cells (TSCs), as well as of the recombination layers in monolithic TSCs. However, the high-energy ITO particles will cause damage to the devices. Herein, the interface reactive sputtering strategy is proposed to construct cost-effective TTEs with high transmittance and excellent carrier transporting ability. Polyethylenimine (PEI) is chosen as the interface reactant that can react with sputtered ITO nanoparticles, so that, coordination compounds can be formed during the deposition process, facilitating the carrier transport at the interface of C60/PEI/ITO. Besides, the impact force of energetic ITO particles is greatly alleviated, and the intactness of the underlying C60 layer and perovskite layer is guaranteed. Thus, the prepared semitransparent subcells achieve a significantly enhanced power conversion efficiency (PCE) of 19.17%, surpassing those based on C60/ITO (11.64%). Moreover, the PEI-based devices demonstrate excellent storage stability, which maintains 98% of their original PCEs after 2000 h. On the strength of the interface reactive sputtering ITO electrode, a stacked all-perovskite TSC with a PCE of 26.89% and a monolithic perovskite-organic TSC with a PCE of 24.33% are successfully fabricated.

Photo-Cross-Linked Fullerene-Based Hole Transport Material for Moisture-Resistant Regular Fullerene Sandwich Perovskite Solar Cells

Despite the high efficiencies currently achieved with perovskite solar cells (PSCs), the need to develop stable devices, particularly in humid conditions, still remains. This study presents the synthesis of a novel photo-cross-linkable fullerene-based hole transport material named FT12. For the first time, the photo-cross-linking process is applied to PSCs, resulting in the preparation of photo-cross-linked FT12 (PCL FT12). Regular PSCs based on C60-sandwich architectures were fabricated using FT12 and PCL FT12 as dopant-free hole transport layers (HTLs) and compared to the reference spiro-OMeTAD. The photovoltaic results demonstrate that both FT12 and PCL FT12 significantly outperform pristine spiro-OMeTAD regarding device performance and stability. The comparison between devices based on FT12 and PCL FT12 demonstrates that the photo-cross-linking process enhances device efficiency. This improvement is primarily attributed to enhanced charge extraction, partial oxidation of the HTL, increased hole mobility, and improved layer morphology. PCL FT12-based devices exhibit improved stability compared to FT12 devices, primarily due to the superior moisture resistance achieved through photo-cross-linking.

Transparent Recombination Electrode with Dual-Functional Transport and Protective Layer for Efficient and Stable Monolithic Perovskite/Organic Tandem Solar Cells

Rational selection and design of recombination electrodes (RCEs) are crucial to enhancing the power conversion efficiency (PCE) and stability of monolithic tandem solar cells (TSCs). Sputtered indium tin oxide (ITO) with high conductivity and excellent transmittance is introduced as RCE in perovskite/organic TSCs. To prevent high-energy ITO particles destroy the underlying material during sputtering, dual-functional transport and protective layer (C1) is employed. The styryl group in C1 can be thermally crosslinked to serve as a sputtering protective layer. Meanwhile, the conjugated phenanthroline skeleton in C1 shows high electron mobility and hole blocking capability to promote the electron transport process at the interfaces and effectively reduce charge accumulation. Monolithic perovskite/organic TSC with high PCE of 24.07% and excellent stability is demonstrated by stacking a 1.77 eV bandgap perovskite layer and a 1.35 eV bandgap organic active layer. This strategy provides new insights for overcoming the fundamental efficiency limits of single-junction devices and promotes the further development of TSC devices.

Buried Interface Passivation: A Key Strategy to Breakthrough the Efficiency of Perovskite Photovoltaics

Owing to the merits of low cost and high power conversion efficiency (PCE), perovskite solar cells (PSCs) have become the best candidate to replace the commonly used silicon solar cells. However, PSCs have been slow to enter the market for a number of reasons, including poor stability, high toxicity, and rigorous preparation process. Passivation strategies including surface passivation and bulk passivation have been successfully applied to improve the device performance of PSCs. The passivation of the defects at the buried interface, which is regarded as a key strategy to breakthrough the device efficiency and stability of PSCs in the future, is ongoing with challenge. Herein, in detail the recent passivation of the buried interface is introduced from three aspects: perovskite layer, buried interlayer, and transport layer. The passivation effect of the buried interface is clearly demonstrated through three categories of salts, organics, and 2D materials. In addition, the transport layer is classified into electron transport layer (ETL) and hole transport layer (HTL). These classifications can help to have a clear understanding of substances which generate passivating effect and guide the continuous promotion of the follow-up buried interface passivating work.

Hexachlorotriphosphazene-assisted buried interface passivation for stable and efficient wide-bandgap perovskite solar cells

Large open-circuit voltage (V_oc) loss is the main issue limiting the efficiency improvement in wide bandgap perovskite solar cells (PerSCs). Herein, a facile buried interface treatment by hexachlorotriphosphazene is developed to suppress the V_oc loss. The PerSCs include a [Cs_0.22FA_0.78Pb(I_0.85Br_0.15)₃]_0.97(MAPbCl₃)_0.03 (1.67 eV) absorber and deliver an efficiency of 21.47% and a V_oc of 1.21 V (V_oc loss of 0.46 V). More importantly, the unencapsulated PerSCs maintain 90% of the initial efficiency after aging 500 h in N₂.

Kinetic Control of Solvate Intermediate Evolution for High-Performance Perovskite Solar Cells by the Facial Mask Incubation Technique

The growth of high-quality perovskite films is complicated by the fact of uncontrollable crystallization pathways from perovskite precursors. During solution processing, extensive undesired nonperovskite products including residual solvate intermediates are produced due to quick solvent evaporation, which will adversely affect the efficiency and stability of perovskite solar cells (PSCs). Herein, we developed a highly efficient phase-transition pathway using a polydimethylsiloxane (PDMS)-based facial mask (FM) incubation technique, which enables significant reduction of the perovskite crystallization rate and depression of perovskite aggregation behavior. A surprising finding reveals that this technique induces complete phase transition from solvate intermediates to the perovskite phase, thereby obtaining phase-pure perovskite film. Meanwhile, a high-quality perovskite film with a shiny smooth surface, decreased defect states, and alleviated lattice strain is achieved after utilizing the FM strategy. Consequently, the target-inverted PSCs deliver a respectable efficiency of ∼21% and superior stability in both shelf storage (over 3700 h with 90% of initial efficiency) and light soaking (over 1000 h with 80% of initial efficiency) conditions. Our work highlights the importance of eliminating residual solvate intermediates to construct high-quality perovskites with excellent phase purity for ongoing production of high-performance perovskite-based optoelectronic devices.

Thermal degradation of the bulk and interfacial traps at 85 °C in perovskite photovoltaics

The facile formation of defects in halide perovskite has recently been regarded as the main bottleneck for both the efficiency and stability of perovskite solar cells (PSCs). Therefore, understanding and controlling defects and traps in PSCs is essential to achieving stable devices. Herein, the thermal degradation of perovskite solar cells at 85 °C is studied in terms of electronic traps and device performance, of which the correlations are discussed. In particular, the shifts and changes in both energetic and spatial distributions of electronic defects are observed by capacitance plus impedance analyses under thermal stress. As the energy level and density of deep traps are quantitatively investigated, both the relaxation and degradation of the traps are identified at different timescales. Additionally, the trap densities are individually traced by positions during thermal degradation, where distinct evolutions are visualized. Notably, the traps are measured dominant at the interface between the perovskite and electron-transport layer (ETL). However, LiF incorporation mitigates the electronic traps by an order of magnitude at both interfaces throughout the thermal degradation, indicating that LiF incorporation reduces the initial trap density and suppresses the further formation of traps near the interfaces.