Naotaka Fujikawa

CH3NH3SnxPb(1–x)I3 Perovskite Solar Cells Covering up to 1060 nm

We report photovoltaic performances of all-solid state Sn/Pb halide-based perovskite solar cells. The cell has the following composition: F-doped SnO2 layered glass/compact titania layer/porous titania layer/CH3NH3SnxPb(1-x)I3/regioregular poly(3-hexylthiophene-2,5-diyl). Sn halide perovskite itself did not show photovoltaic properties. Photovoltaic properties were observed when PbI2 was added in SnI2. The best performance was obtained by using CH3NH3Sn0.5Pb0.5I3 perovskite. 4.18% efficiency with open circuit voltage 0.42 V, fill factor 0.50, and short circuit current 20.04 mA/cm(2) are reported. The edge of the incident photon to current efficiency curve reached 1060 nm, which was 260 nm red-shifted compared with that of CH3NH3PbI3 perovskite solar cells.

Fine tuning the structure of unsymmetrical squaraine dyes towards the development of efficient dye-sensitized solar cells

Creation of molecular asymmetry in the organic sensitizing dyes has been demonstrated for enhancing the photoconversion efficiency due to unidirectional flow of electron after the photoexcitation. Molecular structures for direct indole ring carboxy-functionalized unsymmetrical squaraine dyes have been optimized by fine tuning the molecular structures and judicious selection of the substituents to prevent the dye aggregation and electron recombination. Best efficiency of 4.42 % was achieved for unsymmetrical squaraine dye SQ-64 with a short circuit current density of 11.22 mA/cm2, a fill factor of 0.61 and an open circuit voltage of 0.64 V under standard AM 1.5 simulated solar irradiation.

Tandem Dye-Sensitized Solar Cells Based on TCO-less Back Contact Bottom Electrodes

Mechanically stacked and series connected tandem dye sensitized solar cells (T-DSSCs) are fabricated in novel architectures. The architecture consist of TCO tandem DSSCs stacked with TCO-less back contact DSSCs as bottom electrodes (TCO-less tandem DSSCs). Resulting TCO-less tandem DSSCs architecture finds its usefulness in efficient photon harvesting due to improved light transmission and enhanced photons reaching to the bottom electrodes. The fabricated tandem performance was verified with visible light harvesting model dyes D131 and N719 as a proof of concept and provided the photoconversion efficiency (PCE) of 6.06% under simulated condition. Introduction of panchromatic photon harvesting by utilizing near infrared light absorbing Si-phthalocyanine dye in combination with the modified tandem DSSC architecture led to enhancement in the PCE up to 7.19%.

Combining novel device architecture and NIR dye towards the fabrication of transparent conductive oxide-less tandem dye sensitized solar cells

Tandem solar cells with different device architectures utilizing a back contact transparent conductive oxide-less bottom electrode (TCO-less tandem DSSC) that has better control of the optical transmission losses incurred by intermediate TCO layers with flexible Pt/tin-doped indium oxide (ITO)-polyethylene terephthalate film as an intermediate layer are reported. The proposed device architecture suppresses the optical loss to a greater extent (around 30%). Sensitizers were ruthenium-based N719 dye in the top electrode, while the newly synthesized phthalocyanine dye (PC25) corresponding to photon harvesting in the near infrared (NIR) region (up to 900 nm) was used in the TCO-less bottom cell. Open circuit voltage (Voc) ≥ 1.18 V (sum of top cell and bottom cell Voc) justifies the TCO-less tandem DSSC formation.

Dye-sensitized solar cells based on axially ligated phosphorus-phthalocyanine dyes

Dye-sensitized solar cells with axially anchored phosphorous-phthalocyanine dyes were fabricated for the first time. Although the phosphorus-phthalocyanine dyes do not have a conventional anchoring group (–COOH), these dyes could be absorbed on a TiO2 semiconductor surface. After the optimization of energy levels, a 24% incident photon-to-current efficiency (IPCE) was observed at 710 nm with an IPCE curve edge of 800 nm. The efficiency was 2.67%, which was higher than those of previously reported dye-sensitized solar cells with axially anchored phthalocyanine dyes (less than 1%).

All-solid Sn/Pb halide perovskite sensitized solar cells

We have succeeded in harvesting energy in near infrared region (NIR) by using air stable Sn doped metal halide perovskite materials. The edge of the incident photon to current efficiency (IPCE) edge reached 1060 nm. 4.18 % efficiency is reported. The photovoltaic performance was compared with Pb halide perovskite solar cell with 14.4% efficiency, leading to the conclusion that the low FF and Voc are associated with low shunt resistance (Rsh). One of the methods to suppress the charge recombination will be reported, which includes passivation of porous titania surface states with aminoacid HI salts. The relationship among the surface states of titaniaor alumina, and crystallinity of the perovskites induced by surface passivation molecules, and photovoltaic performances are discussed.

Parametric Optimization of Experimental Conditions for Dye-Sensitized Solar Cells based on Far-red Sensitive Squaraine Dye

A far-red sensitive unsymmetrical squaraine dye SQ-41 has been synthesized and subjected to the fabrication of dye-sensitized solar cells by varying the various parameters in order attain optimum photoconversion efficiency (η). It has been demonstrated that an optimum ratio of dye to coadsorber, thickness of mesoporous TiO2 layer, redox electrolyte and surface treatment are necessary to enhance overall external η. In the case of surface treatment, it has been shown to exhibit pronounced device performance when both of the FTO as well mesoporous TiO2 surfaces were treated with aqueous TiCl4. In spite of very high molar extinction coefficient of dye SQ-41, 10-12 µm thickness of mesoporous TiO2 was found to be necessary to attain the maximum η.

Dye Sensitized Solar Cells Based on Novel Far Red Sensitizing Unsymmetrical Squaraine Dye Containing Pyrroloquinoline Moiety

A novel far-red sensitive and direct aromatic ring carboxy functionalized unsymmetrical squaraine dye based on pyrroloquinoline moiety has been synthesized for the application as sensitizer of dye sensitized solar cells. This dye bearing the characteristics of both of indole and quinoline moieties exhibits the photon harvesting up to 820 nm. The enhancement in the photon harvesting window by the pyrroloquinoline based squaraine dye was attributed to the presence of increased π-conjugation in its pyrroloquinoline donor part. This pyrroloquinoline bearing unsymmetrical squaraine dye exhibits a short circuit current density of 9.88 mA/cm2, an open circuit voltage of 0.57 V and fill factor of 0.59 leading to the external power conversion efficiency of 3.33% under simulated solar irradiation of 100 mW/cm2 at AM 1.5 condition.

Sn halide based perovskite sensitized solar cells covering up to 1060 nm (presentation video)

We have succeeded in harvesting energy in the NIR region by using Sn halide based perovskite materials. The cell has the following composition: F-doped SnO2 layered glass/compact titania layer/porous titania layer/Sn based perovskite material/ p-type polymer semiconductor. The edge of the incident photon to current efficiency (IPCE) edge reached 1040 nm. 4.18 % efficiency with open circuit efficiency (Voc):0.42 V, fill factor (FF): 0.5, short circuit current (Jsc): 20.04 mA/cm2 is reported.