Leif Häggman

Frustrated Lewis pair-mediated recrystallization of CH3NH3PbI3 for improved optoelectronic quality and high voltage planar perovskite solar cells

Films of the hybrid lead halide perovskite CH3NH3PbI3 were found to react with pyridine vapor at room temperature leading to complete bleaching of the film. In dry air or nitrogen atmosphere recrystallization takes place, leading to perovskite films with markedly improved optical and photovoltaic properties. The physical and chemical origin of the reversible bleaching and recrystallization mechanism was investigated using a variety of experimental techniques and quantum chemical calculations. The strong Lewis base pyridine attacks the CH3NH3PbI3. The mechanism can be understood from a frustrated Lewis pair formation with a partial electron donation of the lone-pair on nitrogen together with competitive bonding to other species as revealed by Raman spectroscopy and DFT calculations. The bleached phase consists of methylammonium iodide crystals and an amorphous phase of PbI2(pyridine)2. After spontaneous recrystallization the CH3NH3PbI3 thin films have remarkably improved photoluminescence, and solar cell performance increased from 9.5% for as-deposited films to more than 18% power conversion efficiency for recrystallized films in solar cells with planar geometry under AM1.5G illumination. Hysteresis was negligible and open-circuit potential was remarkably high, 1.15 V. The results show that complete recrystallization can be achieved with a simple room temperature pyridine vapor treatment of CH3NH3PbI3 films leading to high quality crystallinity films with drastically improved photovoltaic performance.

Solid-state dye-sensitized solar cells based on poly(3,4-ethylenedioxypyrrole) and metal-free organic dyes.

Poly(3,4-ethylenedioxypyrrole) (PEDOP), combined with metal-free organic sensitizers, is efficiently used for the first time as the hole-transporting material in solid-state dye-sensitized solar cells. Devices employing PEDOP as the hole conductor and D35 or D21 L6 as the sensitizer show a ten-times-higher energy-conversion efficiency (of 4.5% and 3.3%, respectively) compared to Ru-Z907-based devices. This is due to the efficient suppression of electron recombination.

Investigation of cobalt redox mediators and effects of TiO2 film topology in dye-sensitized solar cells

One-electron outer-sphere redox couples, such as cobalt metal-organic complexes, represent an interesting alternative as redox mediators in dye-sensitized solar cells since they show weak visible l ...

Development of hybrid organic-inorganic materials for efficient charging/discharging in electrochemical and photoelectrochemical capacitors

A composite system of poly (3,4-ethylenedioxythiophene)/multi-walled carbon nanotubes has been investigated and characterized as a potential charge storage material for coupled dye-sensitized solar cell/electrochem. capacitor systems. The selected material can easily operate in org. media (lithium triflate/propylene carbonate) giving a specific capacitance of 95 F g-1 and energy d. of 3.1 Wh kg-1. The combination of the composite material with dye-sensitized solar cell allows to obtain a photo-rechargeable supercapacitor (photocapacitor), destined to work with dies required org. media (here with N 719 dye). The photocapacitor system was built from mesoporous TiO2 electrode, typical charge relay consisting of iodine/iodide redox couple and two charge storage electrodes sepd. by a liq. electrolyte. The system was tested under light illumination of 100 mW cm-2 with xenon lamp equipped with cut-off filters eliminating the UV and IR part of the spectra.

Enhanced charge carrier extraction by a highly ordered wrinkled MgZnO thin film for colloidal quantum dot solar cells

Efficient charge carrier extraction from a colloidal quantum dot (CQD) solid is crucial for high performance of CQD solar cells (CQDSCs). Herein, highly ordered wrinkled MgZnO (MZO) thin films are demonstrated to improve the charge carrier extraction of PbS CQDSCs. The highly ordered wrinkled MZO thin films are prepared using a low-temperature combustion method. The photovoltaic performances of CQDSCs with a combustion-processed MZO (CP-MZO) thin film as an electron transport material (ETM) are compared to those of CQDSCs with a conventional sol–gel processed MZO (SGP-MZO) thin film as an ETM. We performed photoluminescence quenching measurements of the colloidal quantum dot (CQD) solid and charge carrier dynamic analysis of full solar cell devices. The results show that the highly ordered wrinkled CP-MZO thin film significantly increases the charge carrier extraction from the CQD solid and therefore diminishes the charge interfacial recombination at the CQD/ETM junction, leading to a 15.5% increase in power conversion efficiency. The improved efficiency in the CP-MZO based CQDSC is also attributed to the compact and pin-hole free CP-MZO thin film.