Facile Tailoring of Metal‐Organic Frameworks for Förster Resonance Energy Transfer‐Driven Enhancement in Perovskite Photovoltaics

Abstract Förster resonance energy transfer (FRET) has demonstrated its potential to enhance the light energy utilization ratio of perovskite solar cells by interacting with metal‐organic frameworks (MOFs) and perovskite layers. However, comprehensive investigations into how MOF design and synthesis impact FRET in perovskite systems are scarce. In this work, nanoscale HIAM‐type Zr‐MOF (HIAM‐4023, HIAM‐4024, and HIAM‐4025) is meticulously tailored to evaluate FRET's existence and its influence on the perovskite photoactive layer. Through precise adjustments of amino groups and acceptor units in the organic linker, HIAM‐MOFs are synthesized with the same topology, but distinct photoluminescence (PL) emission properties. Significant FRET is observed between HIAM‐4023/HIAM‐4024 and the perovskite, confirmed by spectral overlap, fluorescence lifetime decay, and calculated distances between HIAM‐4023/HIAM‐4024 and the perovskite. Conversely, the spectral overlap between the PL emission of HIAM‐4025 and the perovskite's absorption spectrum is relatively minimal, impeding the energy transfer from HIAM‐4025 to the perovskite. Therefore, the HIAM‐4023/HIAM‐4024‐assisted perovskite devices exhibit enhanced EQE via FRET processes, whereas the HIAM‐4025 demonstrates comparable EQE to the pristine. Ultimately, the HIAM‐4023‐assisted perovskite device achieves an enhanced power conversion efficiency (PCE) of 24.22% compared with pristine devices (PCE of 22.06%) and remarkable long‐term stability under ambient conditions and continuous light illumination.

Synthesis of HIAM-4023: 20.0 mg ZrOCl2•8H2O, 10 mg H4ABTTC linkers, 0.30 mL formic acid, and 3 mL DMF were added in a 5 mL vial.The mixture was sonicated for several minutes and then put into the 90°C preheated oven for 30 minutes.After cooling down to room temperature, the formed nano-MOFs were obtained by centrifugation at 11000 rpm for 10 minutes, which was washed using DMF and methanol for three times.
Synthesis of HIAM-4024: 20.0 mg ZrOCl2•8H2O, 10 mg H4BTATC linkers, 0.35 mL formic acid, and 3 mL DMF were added in a 5 mL vial.The mixture was sonicated for several minutes and then put into the 90°C preheated oven for 30 minutes.After cooling down to room temperature, the formed nano-MOFs were obtained by centrifugation at 11000 rpm for 10 minutes, which was washed using DMF and methanol for three times.
Synthesis of HIAM-4025: 20.0 mg ZrOCl2•8H2O, 10 mg H4NSATC linkers, 0.50 mL formic acid, and 3 mL DMF were added in a 5 mL vial.The mixture was sonicated for several minutes and then put into the 90°C preheated oven for 30 minutes.After cooling down to room temperature, the formed nano-MOFs were obtained by centrifugation at 11000 rpm for 10 minutes, which was washed using DMF and methanol for three times.
were sequentially rinsed by sonication in detergent, deionized (DI) water, acetone, and ethanol, and finally dried in the air by nitrogen flow.Before the deposition of ETL, ITO substrates were exposed to UV-ozone for 30 min.A thin layer of SnO2 nanoparticle film was spin-coated on the ITO substrate at 4,000 r.p.m. for 30 s to form a 50-nm-thick ETL and annealed in ambient air at 150 °C for 30 min.
Then, the perovskite layer was deposited on the SnO2 layer by a two-step spin-coating method.
The PbI2-HIAM-MOF precursor solution was prepared by dissolving 1.4 M PbI2 into the mixed solvent of DMF and DMSO (4.5:0.5, v/v) in a nitrogen-filled glove box.The dissolved solution was filtered with the filter (0.22μm, Oriental Chemicals).The filtered PbI2 solution added HIAM-4023, HIAM-4024, and HIAM-4025 powder and sealed sonicated for 30 min.The PbI2 precursor solution was first spin-coated on the glass at 1500 rpm for 30 s.The substrate with the newly deposited PbI2 layer was annealed at 70 °C for 1 min.After the PbI2 film cooled down to room temperature, 40 μL of the organic mixture solution of FAI: MACl: MABr (60: 6: 6 mg in 1 mL IPA) was spin-coated onto the PbI2 during spinning at 1800 rpm for 30 s.When the resulting film turned from orange to dark brown in drying, they were thermally annealed at 130 °C for 30 min under ambient conditions.Filtered spiro-OMeTAD solution (72.3 mg dissolved in 1 mL chlorobenzene) with 30 µL of tBP and 35 µL of Li-TFSI (260 mg mL −1 in acetonitrile) was spin-coated on the top of the perovskite layer at 4000 rpm for 30 s in a glove box after the substrates cooling down to room temperature.
Finally, 90-100 nm of gold was deposited by thermal evaporation on top of the HTL layer to complete the device, using a shadow mask to pattern the electrodes.The active area of the cells was 0.09 cm 2 , which was defined by the overlapped area of the Au electrode and the ITO stripe.
GIWAXS measurement: GIWAXS measurements were performed at the Synchrotron & Printable Electronic Lab, Hoffmann Institute of Advanced Materials, Shenzhen Polytechnic 500K detector.The incidence angle is 0.5°.
Characterization: The J-V characteristics of the devices were measured using a B1500 A semiconductor parameter analyzer under the calibrated ABET Technologies SUN 2000 solar simulator equipped with an AM 1.5 filter at 100 mW cm −2 .
The corresponding IPCE spectrum was measured in air by a QE-R3011 system from Enli Technology Co. Ltd. (Enli).
The morphologies of PSCs were investigated by a high-resolution field emission SEM (JEOL JSM-6335F).
PL spectrum and TRPL signals of perovskite film were recorded by using Edinburgh FLSP920 spectrophotometer equipped with the excitation source of 465 nm picosecond pulsed diode laser.
Photoluminescence quantum yield (PLQY) was measured on a C9920-03 absolute quantum yield measurement system (Hamamatsu Photonics) with a 150 W xenon monochromatic light source and 3.3 inch integrating sphere.
Where e denotes elementary charge, L represents the thickness of the perovskite film, ε means the relative dielectric constant of perovskite, and ε0 indicates the vacuum permittivity.VTFL is the onset voltage of the trap-filled limit region.

Figure S3 .Figure S4 .
Figure S3.The fluorescence lifetime curves and fitting profiles of coexpressed HIAM-MOF with and without perovskite, in conjunction with the experimental instrument response function (IRF) for HIAM-4023, HIAM-4024, and HIAM-4025.(Repeated TRPL experiments were conducted five times for each of the six materials.)

Figure S5 .
Figure S5.Photographs of the PbI2 precursor solutions with pristine and HIAM-MOF-assisted.

Figure S13 .
Figure S13.Mott-Schottky plots of the devices reveal the interfacial charge density for the pristine and HIAM-4023-assisted devices.

Figure S14 .
Figure S14.Current density-voltage (J-V) curves of the pristine and different concentrations of HIAM-4023assisted devices.

Table S1 .
The recent summary report on the energy transfer occurring between MOFs and perovskites.

Table S3 .
Photovoltaic parameters of PSCs with control and different concentrations of HIAM-4023 under AM 1.5G illumination at 100 mW cm -2 .