Junnian Chen

High performance organic sensitizers based on 11,12-bis(hexyloxy) dibenzo[a,c]phenazine for dye-sensitized solar cells

Three new metal-free organic sensitizers containing 11,12-bis(hexyloxy) dibenzo[a,c]phenazine (BPz) units were synthesized and used for dye-sensitized solar cells (DSSCs). The broad absorption spectra indicate that the light harvesting abilities were enhanced by the introduction of the BPz unit in the π-conjugated space, which can also cause an anti-aggregation effect and the suppression of charge recombination. Among these sensitizers, LI-39 showed the best photovoltaic performance: a short-circuit photocurrent density (Jsc) of 14.40 mA cm−2, an open-circuit photovoltage (Voc) of 0.74 V, and a fill factor (ff) of 0.67, corresponding to an overall conversion efficiency of 7.18% under standard global AM 1.5 solar light conditions. The result shows that the organic sensitizers based on this bulky fused aromatic rings as well as the auxiliary acceptor are the promising candidates for improvement of the performance of DSSCs.

Iodine-free quasi solid-state dye-sensitized solar cells based on ionic liquid and alkali salt

A novel iodine-free quasi solid-state electrolyte employing an ionic liquid (1, 2-dimethyl-3-propylimidazolium iodide, DMPII) as charge transfer intermediate was developed for dye-sensitized solar cells (DSSCs). Simultaneously, potassium iodide (KI) was incorporated into the electrolyte as charge transfer auxiliary agent. The dependences of photovoltaic performances and ionic conductivities on the iodine-free quasi solid-state electrolyte containing different KI concentrations were investigated. The strong interactions between the potassium cations and polyethylene oxide (PEO, MW = 100,000) can prevent the crystallization of the electrolyte and enhance its ionic conductivity. An optimal photoelectric conversion efficiency (η) of 5.87% can be obtained for the DSSC fabricated with the iodine-free electrolyte containing 5 wt% KI, and the corresponding value without KI is 4.05%, indicating the remarkable progress made by addition of KI into electrolyte.

Self-organized film of ultra-fine TiO2 nanotubes and its application to dye-sensitized solar cells on a flexible Ti-foil substrate

One dimensional structures of TiO2 (nanowires and nanotubes) are promising for dye-sensitized solar cells due to reduced electron recombination; however, the small surface area is the main hurdle in the application of one dimensional anatase structures to dye-sensitized solar cells because of insufficient dye adsorption. Here, we address this problem with the preparation of a TiO2 nanotube film with a high specific surface area. This film was self-assembled by ultra-fine TiO2 nanotubes with diameter <10 nm via a simple hydrothermal method, and was applied to dye-sensitized solar cells on flexible Ti metal using a transplanting technique. Due to the higher surface area and one-dimensional structure, 6.23% efficiency was obtained with this ultra-fine TiO2 nanotube film, which was superior to that of conventional TiO2 nanoparticles.

Low-cost, quasi-solid-state and TCO-free highly bendable dye-sensitized cells on paper substrate

A highly conductive Ni-coated commercial paper substrate (square resistance <1 Ω) was prepared by chemical deposition, and used as the substrate for a flexible TiO2 film electrode derived from a binder-free TiO2 paste, and heat treated at 250 °C. A low-cost, quasi-solid-state and TCO-free highly bendable paper-based dye-sensitized solar cell with conversion efficiency up to 2.90% is fabricated successfully by applying an iodine-free electrolyte. This encouraging result indicates that commercial paper is a promising material for use in dye-sensitized solar cells because of its flexibility, low cost and relatively high resistance to temperature. Compared with the rigid transparent conducting oxide (TCO) coated glass and flexible conductive plastic substrates, the potential of using mature paper making and coating technologies will greatly reduce the cost of the current photovoltaic devices.

New anthracene-based organic dyes: the flexible position of the anthracene moiety bearing isolation groups in the conjugated bridge and the adjustable cell performance

Three organic sensitizers (LI-65–LI-67), featuring a 9,10-diarylsubstituted anthracene unit as part of the conjugated bridge, were designed and employed in dye-sensitized solar cells (DSCs). The two phenyl groups on the 9 and 10 positions of the anthracene ring acted as isolation groups, to suppress possible dye aggregation and electron recombination. With the flexible position of the isolation group in the conjugated bridge, interesting structure–property relationships were obtained: the isolation groups (the phenyl rings on the anthracene unit), close to the donor, were beneficial to the enhancement of the short circuit current (Jsc) values, with the highest Jsc value of 13.95 mA cm−2 (LI-65); once located in the middle of the π-bridge, the highest resistance of charge recombination and the longest electron lifetime were achieved and contributed to the enhanced open circuit voltage (Voc) of 722 mV, with the highest conversion efficiency (η) of 6.44% (LI-66, 25% higher than the lowest).