Metal–Organic Framework Thin Film-Based Dye Sensitized Solar Cells with Enhanced Photocurrent

Metal–organic framework thin film-based dye sensitized solar cell is fabricated with highly oriented, crystalline, and porous Zn-perylene metal-organic framework (MOF) thin film (SURMOF) which is integrated with Bodipy embedded in poly(methyl methacrylate). It has been demonstrated that the photocurrent can be enhanced by a factor of 5 relative to Zn-perylene MOF thin film due to triplet–triplet annihilation up-conversion between the Bodipy/PMMA sensitizer and the Zn-perylene MOF thin film acceptor using Co(bpy)32+/3+ as redox mediator.


Materials
All the chemicals were purchased from Sigma Aldrich. The TiO2 18-NRT is purchased from Heptachroma Company. All the used chemicals are analytically pure and used as received.

Methods
The NMR spectra were recorded with OXFPRD NMR 400 MHz spectrometer using CDCl3 as solvent and tetramethylsilane (TMS) as standard at 0.00 ppm. HRMS was accomplished with matrix-assisted laser desorption/ ionization (MALDI) micro MALDI TOF mass spectrometer (Waters, U.K.). The Nanosecond transient absorption spectroscopy was measured with a LP920 laser flash photolysis spectrometer (Edinburgh Instruments, Livingston, U.K.). Firstly, the samples were purged with N2 for 15 min before measurements, and the N2 gas flow was kept constant during the measurement. The signal was digitized with a Tektronix TDS 3012B oscilloscope. The UV-Vis measurement was recorded with Agilent 8453 instrument. The fluorescence spectra of Zn-perylene SURMOFs were measured with a spectroflourometer (Flouromax-4 spectroflourometer-Horiba. Laser sources for our experiments are purchased from Changchun New Industries ptoelectronics Technology Co., Ltd. Green Laser). The infrared spectra of the SURMOF sample were obtained with a resolution of 2 cm-1 with FTIR spectrometer (Bruker VERTEX 80v) under vacuum (~3 mbar) equipped with a liquid nitrogen cooled narrow band mercury cadmium telluride (MCT) detector. The 3,9-perylenedicarboxylic acid reference samples were prepared into a KBr pellet and measured in transmission mode. The i−t curves were recorded with a potentiostat (CHI 660D, Shanghai, China) using diode pumped solid state (DPSS) continuous laser (530 nm, 430 nm) (Changchun New Industries Optoelectronics Technology Co., Ltd. Green Laser). The dye sensitized solar cells having two electrode system consisting of SURMOFs sample as working electode and Pt-electrode as counter electrode were used. The SHIMAZDU spectrofluorophotometer (RF-5301pc) with laser sources was used for the upconversion. The power of the laser beam was measured with VLP-2000 pyroelectric laser power meter.

Synthesis of Bodipy derivative
The Bodipy derivative 3 was synthesized according to the scheme as shown in Scheme 1.
1 was synthesized according to literature methods 1 .
2 was synthesized according to literature methods 2 .

Preparation of FTO/TiO2-Zn-Perylene SURMOF-Bodipy/PMMA
First, 40 mg/mL PMMA was prepared in the acetonitrile solution. Subsequently, pyridine functionalized Bodipy with a concentration of 30 M was added into the aforementioned PMMA solution. Then, the FTO-TiO2-Zn-perylene SURMOF was immersed into the mixture of PMMA and Bodipy solution for one hour. During immersion, the solution was bubbled with N2 under light irradiation. Finally, after drying with N2, the Bodipy/PMMA layer was formed on top of FTO/TiO2-Zn-perylene SURMOF as shown in Figure S2. The thickness of Bodipy/PMMA is dependent on the color change on the surface of Zn-perylene SURMOF which is shown in Figure S3.

Photoelectrochemical characterization
The i−t curves were recorded with a potentiostat using the DSSC-like device using FTO-TiO2-Zn-perylene SURMOF-Bodipy/PMMA, FTO-TiO2-Zn-perylene SURMOF and FTO-TiO2-Bodipy/PMMA as working electrode, Pt as counter electrode and Co(bpy)3 2+ / 3+ in acetonitrile as electrolyte. A 530 nm green laser and a 430 nm green laser were used for light irradiations Figure S1. 1H         . Emission spectra of perylene dicarboxylic acid (blue, λex = 430 nm) and perylene dicarboxylic acid + Bodipy (green, λex = 532 nm) in deaerated acetonitrile solution. The 532-nm excitation peak is attributed to the wavelength of laser source. Excitation power density of 4.6 mW/cm 2 was used to for 532 nm laser source. Figure S8. Emission spectra of biphenyl dicarboxylic acid + Bodipy (green, λex = 532 nm) in deaerated acetonitrile solution. The 532-nm excitation peak is attributed to the wavelength of laser source. Excitation power density of 4.6 mW/cm 2 was used to for 530-nm laser source.