D-pi-A Dye System Containing Cyano-Benzoic Acid as Anchoring Group for Dye-Sensitized Solar Cells

A D-pi-A dye (KM-1) incorporating cyanobenzoic acid as a new acceptor/anchoring group has been synthesized for dye-sensitized solar cells (DSCs) with a high molar extinction coefficient of 66 700 M-1 cm(-1) at 437 nm. Theoretical calculations show that the hydrogen bond between -CN and surface hydroxyl leads to the most stable configuration on the surface of TiO2. In addition, the adsorption of the dye on TiO2 follows a Brunauer-Emmett-Teller (BET) isotherm. Multilayer adsorption of KM-1 on TiO2 seems to take place particularly at higher dye concentrations. DSC device using KM-1 reached a maximum incident photon-to-current conversion efficiency (IPCE) of 84%, with a solar to electric power conversion efficiency (PCE) of 3.3% at AM1.5 G illumination (100 mW cm(-2)). This new type of anchoring group paves a way to light harvesting with strong binding to the metal oxide surface. design new dyes that combine good visibl

Influence of the Anchoring Modes on the Electronic and Photovoltaic Properties of D−π–A Dyes

Five new donor−π-bridge−acceptor (D−π−A) organic sensitizers with cyano and/or triple bond substituted benzoic acid as acceptor/anchoring groups were synthesized and tested for their performance in dye-sensitized solar cells (DSCs). The systematic incorporation of a cyano group on the benzoic acid anchoring part and an additional acetylene bond at the para-position to −COOH lead to a variation of the photoelectrochemical properties, electronic transitions, and device performances. Characterization of the molecular structure, the electronic/optical properties of the dyes, as well as their photovoltaic performance in DSCs was accomplished by means of electrochemistry, quantum chemical methods, and various spectroscopic techniques such as photoinduced absorption, steady-state spectroscopy, and time-resolved transient absorption studies on femto- and nanosecond time scales. Thereby, significant dependence of DSCs performances on the substituents and anchoring groups was observed. In general, cyano substituents lead to improved DSCs performances. On the other hand, the insertion of an acetylene linker in combination with a cyano group does not enhance the device efficiencies. Devices composed of a para-cyano benzoic acid as anchor revealed maximum IPCE values of 80% with a PCE of 4.50% at AM 1.5 G illumination (100 mW cm−2) due to retarded charge recombination dynamics

Effect of Extended π-Conjugation of the Donor Structure of Organic D–A−π–A Dyes on the Photovoltaic Performance of Dye-Sensitized Solar Cells

Two new D−A−π-spacer−A organic dyes, KM-10 and KM-11, containing a benzothiadiazole unit in a π-spacer and a cyanoacrylic acid as an acceptor have been synthesized and tested as sensitizers in dye-sensitized solar cells. Structural variations of the donor moiety, i.e., π-extension of the diphenylamine electron-donating groups, gave rise to different photovoltaic efficiencies –7.1% for KM-10 and 8% for KM-11– despite having comparable absorption properties. A detailed investigation, including transient photo- current and photovoltage decay measurement, transient absorption spectroscopy, and quantum chemical methods, provided important conclusions about the nature of the substitution on the photovoltaic properties of dyes

Highly Efficient Mesoscopic Dye-Sensitized Solar Cells Based on Donor-Acceptor-Substituted Porphyrins

To dye for: A porphyrin chromophore, which is integrated into a donor-acceptor dye as a π-conjugated bridge (see picture), exhibits an unprecedented efficiency of 11 □ % when used as a photosensitizer in a double-layer TiO2 film. A greatly enhanced photovoltaic performance is observed when the porphyrin dye is cosensitized with a metal-free dye that has a complementary spectral response. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

A new generation of platinum and iodine free efficient dye-sensitized solar cells

We report a series of cobalt complexes with various polypyridyl ligands, where the oxidation potential is tuned from 0.17 to 0.34 V vs. ferrocene. The highest occupied molecular orbitals (HOMO) of the cobalt complexes were stabilized by adding electron acceptor groups on pyridyl or replacing pyridyl by pyrazole. These complexes are then used as one-electron redox mediators in dye sensitized solar cells (DSSCs) together with polymer based cathode resulting in an excellent performance. The performance of DSSCs using the molecularly engineered cobalt redox shuttle and poly(3,4-alkylthiophenes) based cathode is better than the triiodide/iodide redox shuttle with platinized cathode. The use of high surface area poly(3,4-propylenedioxythiophene) based nanoporous layers allows higher catalytic activity thus minimizing the electrode–electrolyte interface issues

Light scattering enhancement from sub-micrometer cavities in the photoanode for dye-sensitized solar cells

A simple cell architecture that achieves enhanced light harvesting with less dye quantity while simultaneously improving the power conversion efficiency (PCE) of dye-sensitized solar cells is presented. Polystyrene (PS) spheres of sub-micrometer size were incorporated into the titanium dioxide paste resulting in photoanodes with bimodal pore size distribution. Scanning electron micrographs of TiO2 films revealed a mixture of mesoporous and macroporous morphology in which sub-micrometer cavities created by the combustion of PS increased the light scattering, enhancing the optical path length and hence the harvesting of photons by the sensitizer. The amount of dye uptake by these films is lower than that of standard films because the high porosity reduces the total surface area. Even with lower dye adsorption, the photovoltaic performance has been maintained and even improved, mainly due to better open circuit voltage and higher fill factor. Overall, better light harvesting has helped to maintain the efficiency of dye-sensitized solar cells while saving up to 30% of dye loading and replacing the conventional 400 nm scattering layer with voids. By employing these photoanodes, an efficiency of 6.9% was achieved in ionic liquid based dye sensitized solar cells

Interpretation of Optoelectronic Transient and Charge Extraction Measurements in Dye-Sensitized Solar Cells

Tools that assess the limitations of dye sensitized solar cells (DSSCs) made with new materials are critical for progress. Measuring the transient electrical signals (voltage or current) after optically perturbing a DSSC is an approach which can give information about electron concentration, transport and recombination. Here we describe the theory and practice of this class of optoelectronic measurements, illustrated with numerous examples. The measurements are interpreted with the multiple trapping continuum model which describes electrons in a semiconductor with an exponential distribution of trapping states. We review standard small perturbation photocurrent and photovoltage transients, and introduce the photovoltage time of flight measurement which allows the simultaneous derivation of both effective diffusion and recombination coefficients. We then consider the utility of large perturbation measurements such as charge extraction and the current interrupt technique for finding the internal charge and voltage within a device. Combining these measurements allows differences between DSSCs to be understood in terms such as electron collection efficiency, semiconductor conduction band edge shifts and recombination kinetics

Comparative performance analysis of photo-supercapacitor based on silicon, dye-sensitized and perovskite solar cells: Towards indoor applications

The rapid development of the Internet of Things (IoTs) demands self-powered indoor devices to supply continuous power. Thus, developing an efficient photo-storage device that is capable of harvesting and storing indoor light energy requires detailed performance analysis of suitable solar cells. Herein, a comparative study of the performance of photo-storage systems based on three different solar cell technologies in combination with symmetric non-volatile supercapacitors was performed. Considering the advantages of hybrid solar cells such as low-cost fabrication and high photovoltaic response under diffused light, perovskite solar cells (PSCs) and dye-sensitized solar cells (DSCs) were selected, and the photo-storage efficiencies were compared with crystalline silicon solar cells (crystalline Si–SCs) under outdoor (Xe light irradiation: 1–100 mW cm−2) and indoor white Light Emitting Diode (LED) (1–20 mW cm−2) illumination. Photovoltaic performance was compared using current-voltage (IV), maximum power point tracking (MPPT), and charging of supercapacitor, either directly or through a DC-DC converter. The highest efficiencies were observed with PSCs under low light intensity, using Xe light and white LED light conditions. Despite the anomalous hysteresis behavior, IV analysis of the PSCs showed efficiency above 12% under Xe light irradiation and above 20% using white LED lighting (extracted from the reverse scan and at light intensity intervals of 1–20 mW cm−2). The determination of real-time efficiencies at MPP for PSCs showed a temporary efficiency drop at each intensity under white LED light, which is more significant for longer illumination times. However, under low light-intensity, single PSCs showed only a slight average voltage drop of 800 to 700 mV in comparison with a considerable drop of 800 to 500 mV at MPP for two series-connected crystalline Si–SCs. In addition, single PSC was able to show better power delivery efficiencies (PDEs) and supply the required minimum operating voltage for the DC-DC boost converter at 1–20 mW cm−2 where two series solar cells are required for DSCs and crystalline Si–SCs. The overall efficiencies for the DC-DC boost converter charging dropped towards low intensities from 9 to 5% and 8.5 to 2.7% for PSCs and crystalline Si–SCs, respectively. This decrease was mainly due to the loss of converter efficiency at low input powers which could be negligible on large-scale solar cells. Furthermore, in direct charging, PSC provided over 8.5% stable overall efficiencies with about 80% storage efficiency under white LED light intensities ranging from 1 to 20 mW cm−2 at the areal discharge, and were able to maintain high overall peak efficiencies of 5.6 and 4.1% at high areal discharging currents of 18 and 30 mA cm−2, respectively. This study demonstrates the suitability of photo-supercapacitor systems combining PSCs and carbon-based supercapacitors for continuous power-up of indoor high-current-requirement IoT devices