Jianghua Zhao

Structure Engineering of Hole–Conductor Free Perovskite-Based Solar Cells with Low-Temperature-Processed Commercial Carbon Paste As Cathode

Low-temperature-processed (100 °C) carbon paste was developed as counter electrode material in hole-conductor free perovskite/TiO2 heterojunction solar cells to substitute noble metallic materials. Under optimized conditions, an impressive PCE value of 8.31% has been achieved with this carbon counter electrode fabricated by doctor-blading technique. Electrochemical impedance spectroscopy demonstrates good charge transport characteristics of low-temperature-processed carbon counter electrode. Moreover, this carbon counter electrode-based perovskite solar cell exhibits good stability over 800 h.

Dye-Sensitized Solar Cells Based on a Donor-Acceptor System with a Pyridine Cation as an Electron-Withdrawing Anchoring Group

New hemicyanine dyes (CM101, CM102, CM103, and CM104) in which tetrahydroquinoline derivatives are used as electron donors and N-(carboxymethyl)-pyridinium is used as an electron acceptor and anchoring group were designed and synthesized for dye-sensitized solar cells (DSSCs). Compared with corresponding dyes that have cyanoacetic acid as the acceptor, N-(carboxymethyl)-pyridinium has a stronger electron-withdrawing ability, which causes the absorption maximum of dyes to be redshifted. The photovoltaic performance of the DSSCs based on dyes CM101-CM104 markedly depends on the molecular structures of the dyes in terms of the n-hexyl chains and methoxyl. The device sensitized by dye CM104 achieved the best conversion efficiency of 7.0% (J(sc) = 13.4 mA cm(-2), V(oc) = 704 mV, FF = 74.8%) under AM 1.5 irradiation (100 mW cm(-2)). In contrast, the device sensitized by reference dye CMR104 with the same donor but the cyanoacetic acid as the acceptor gave an efficiency of 3.4% (J(sc) =6.2 mA cm(-2), V(oc) = 730 mV, FF = 74.8%). Under the same conditions, the cell fabricated with N719 sensitized porous TiO(2) exhibited an efficiency of 7.9% (J(sc) = 15.4 mA cm(-2) , V(oc) = 723 mV, FF = 72.3%). The dyes CM101-CM104 show a broader spectral response compared with the reference dyes CMR101-CMR104 and have high IPCE exceeding 90% from 450 to 580 nm. Considering the reflection of sunlight, the photoelectric conversion efficiency could be almost 100% during this region.

Molecular Design and Performance of Hydroxylpyridium Sensitizers for Dye-Sensitized Solar Cells

Four hydroxylpyridium organic dyes were synthesized and applied in dye-sensitized solar cells (DSSCs). Hydroxylpyridium was introduced as an electron acceptor in donor-π-conjugated bridge-acceptor (D-π-A) system. The traditional anchoring groups, such as the carboxyl group, were replaced by hydroxyl group. It was found that the existence of the hydroxylpyridium exhibits a large effect on the absorption spectra of dyes JH401-JH404. For JH series of dyes, hexylthiophene was employed as the π-conjugated bridge, and triphenylamine, phenothiazine, and their derivatives were used as the electron donor. The performances of the dyes with different structure were investigated by photophysical, photovoltaic, and electrochemical methods. When applied in the DSSCs, the sensitizer JH401 yields the best efficiency, 2.6% (Jsc = 6.35 mA/cm(2), Voc = 605 mV, FF = 67.6%) under 100 mW/cm(2) light illumination. Its maximum incident photon-to-current conversion efficiency (IPCE) is 80% at 440 nm light wavelength, which is the highest IPCE value achieved with hydroxyl group adsorbent organic dyes so far.

Efficient Dye‐Sensitized Solar Cells Based on Hydroquinone/Benzoquinone as a Bioinspired Redox Couple

A hybrid electrolyte involving tetramethylammonium (TMA) hydroquinone/benzoquinone redox couple is formulated. This electrolyte is more transparent than the traditional I(-)/I(3)(-) electrolyte and has negligible absorption in the visible region. Dye-sensitized solar cells using the hybrid electrolyte show higher light-to-electricity conversion efficiency. FTO=fluorine-doped tin oxide.

Efficient Panchromatic Organic Sensitizers with Dihydrothiazole Derivative as π-Bridge for Dye-Sensitized Solar Cells

Novel organic dyes CC201 and CC202 with dihydrothiazole derivative as π-bridge have been synthesizedand applied in the DSSCs. With the synergy electron-withdrawing of dihydrothiazole and cyanoacrylic acid, these two novel dyes CC201 and CC202 show excellent response in the region of 500-800 nm. An efficiency as high as 6.1% was obtained for the device fabricated by sensitizer CC202 together with cobalt electrolyte under standard light illumination (AM 1.5G, 100 mW cm(-2)). These two novel D-π-A panchromatic organic dyes gave relatively high efficiencies except common reported squaraine dyes.

Effect of the acceptor on the performance of dye-sensitized solar cells

Three new phenothiazine dyes were designed and synthesized, utilizing different acceptor groups. Upon application to TiO2-based solar cells, the effects of different acceptors on the photophysical and electrochemical properties of the dyes and the solar cell performance are detailed. The introduction of a pyridinium unit or 5-carboxy-1-hexyl-2,3,3-trimethyl-indolium unit into the molecular frame as the acceptor instead of cyano acrylic acid can effectively cause a red shift in the absorption spectra. Applied to DSSCs, the devices sensitized by CM502 with the pyridinium unit as the acceptor show the highest efficiency of 7.3%. The devices fabricated with dye CM501 with cyano acrylic acid as the acceptor exhibited the highest Voc while for the devices sensitized by the dye CM503 with 5-carboxy-1-hexyl-2,3,3-trimethyl-3H-indolium unit as the acceptor, the Voc value was the lowest, at 494 mV. The addition of TBP in the electrolyte can improve the performance of DSSCs fabricated using CM501 and CM502, with the Voc value greatly improved but the Jsc value slightly decreased. However, with the addition of TBP in the electrolyte, the efficiency of the cells sensitized by CM503 dropped significantly (from 4.9% to 1.0% when 0.1 M TBP was added).

Phenothiazine derivatives-based D–π–A and D–A–π–A organic dyes for dye-sensitized solar cells

D–π–A and D–A–π–A-structured organic dyes represent different developmental directions of photosensitizers in dye-sensitized solar cells (DSSCs). In this work, two phenothiazine derivatives-based D–π–A and D–A–π–A-structured organic dyes have been synthesized and applied in DSSCs. The physical and electrochemical properties of both dyes have been investigated systematically. The results show that the D–A–π–A-structured dye exhibits a broader spectrum response but lower molar coefficient of extinction when compared to the D–π–A-structured dye. Regarding photovoltaic performance, the D–π–A-structured dye yields a higher efficiency (η) of 7.5% with a higher short-circuit current density (Jsc) of 16.36 mA cm−2 and open-circuit voltage (Voc) of 706 mV than that of the D–A–π–A-structured dye. Incident photon-to-electron conversion efficiency (IPCE) studies and impedance analysis also support these results. These results demonstrate that the phenothiazine derivatives-based D–π–A-structured organic dyes can compete with, and even exceed, D–A–π–A-structured organic dyes under the same test conditions.

Efficient Organic Dye‐Sensitized Solar Cells: Molecular Engineering of Donor–Acceptor–Acceptor cationic dyes

Three metal-free donor-acceptor-acceptor sensitizers with ionized pyridine and a reference dye were synthesized, and a detailed investigation of the relationship between the dye structure and the photophysical and photoelectrochemical properties and the performance of dye-sensitized solar cells (DSSCs) is described. The ionization of pyridine results in a red shift of the absorption spectrum in comparison to that of the reference dye. This is mainly attributable to the ionization of pyridine increasing the electron-withdrawing ability of the total acceptor part. Incorporation of the strong electron-withdrawing units of pyridinium and cyano acrylic acid gives rise to optimized energy levels, resulting in a large response range of wavelengths. When attached to TiO2 film, the conduction band of TiO2 is negatively shifted to a different extent depending on the dye. This is attributed to the electron recombination rate between the TiO2 film and the electrolyte being efficiently suppressed by the introduction of long alkyl chains and thiophene units. DSSCs assembled using these dyes show efficiencies as high as 8.8 %.

Efficient Organic Sensitizers with Pyridine‐N‐oxide as an Anchor Group for Dye‐Sensitized Solar Cells

Five organic dyes with pyridine-N-oxide as the anchor group and electron acceptor have been synthesized and applied in dye-sensitized solar cells (DSSCs). Benzothiadiazole was introduced in the conjugation system to increase the electron withdrawing properties, FTIR spectra showed that the coordination was between the pyridine-N-oxide and the Brønsted acid site on the TiO2 surface. The relationship between different dye structures and the performance of the DSSCs was investigated systematically. The location of the thiophene unit was studied, and the direct linkage of benzothiadiazole with pyridine-N-oxide was beneficial to broaden the absorption. The donor-acceptor-acceptor-configured dye WL307, which has 2-ethylhexyloxy chains in the donor part, showed the best efficiency of 6.08% under 100 mW cm(-2) light illumination. The dye series showed a fairly good stability during the one month test period.

Dye-sensitized solar cells based on hydroquinone/benzoquinone as bio-inspired redox couple with different counter electrodes.

In the present study, tetramethylammonium hydroquinone (HQ)/benzoquinone (BQ) were developed for use as a redox couple, with poly(3,4-ethylenedioxythiophene) (PEDOT) and multiwalled carbon nanotubes (MWNT) being proposed for use as counter electrode (CE) catalysts in dye-sensitized solar cells (DSSCs). Both metal-complex N719 and metal-free organic dye CM309 were employed to fabricate devices. For the devices sensitized by N719, when using PEDOT and MWNT CEs, power conversion efficiencies (PCE) of 5.2 and 4.9% were obtained, respectively, which were much higher than that of the device using the traditional Pt CE (4.7%) when HQ/BQ electrolyte was employed. However, with the HQ/BQ redox shuttle, the efficiency of the devices sensitized by N719 is much lower than that of the devices when the traditional I(-)/I3(-) based electrolyte and Pt CE were employed (7.9%). While for the CM309 sensitized solar cells, when the HQ/BQ redox shuttle was employed, PEDOT and MWNT performed much better than Pt, the DSSC using the PEDOT CE showed an efficiency of 6.2%, which was close to that of the DSSC using the traditional I(-)/I3(-) electrolyte and Pt CE (6.3%).