A Double‐Band Tandem Organic Dye‐sensitized Solar Cell with an Efficiency of 11.5 %

Abstract

In the two decades that have passed since O'Regan and Grät-zel first reported mesoporous nanostructured dye-sensitized solar cells (DSCs) in 1991, great progress has been made. [1] Recently, particular attention has been given to the development of organic dyes and tuning their lowest unoccupied and highest occupied molecular orbital (LUMO and HOMO) levels to match the conduction band (CB) of nanostructured semiconductors and redox potential of the electrolyte, respectively, to increase the total solar energy conversion efficiency. [2][3][4] However, the absorption spectra of most organic dyes reported thus far mainly cover the visiblelight region. [5,6] This has motivated research towards the development of new types of organic dyes [7][8][9][10] with absorption spectra extended to the near-IR and IR region. By adjusting the donor, linker, and acceptor units, our group obtained an organic "black dye" that absorbs panchromatic light up to 920 nm.[11] However, the efficiency of the dye was unsatisfactory owing to a lower photovoltage, caused by a large dark current. Recently, we also developed another series of donor-acceptor organic dyes with lateral carboxylic acid anchoring groups instead of cyanoacetic acid units. This modification afforded near-IR organic dyes.[12] However, this series of dyes did not absorb the in 400-550 nm part of the sunlight spectrum and also showed lower photovoltage.We turn to nature for inspiration on how to overcome these problems and achieve broader dye absorption spectra and lower photovoltages.[13] Two types of chlorophylls are used in natural photosynthesis: P680 to drive the high-voltage water oxidation reaction in Photosystem II; and P700 to drive the relatively low-voltage NADP + reduction in Photosystem I. [14] Motivated by this natural tandem system, we report a tandem DSC [15] in which the front sub-cell employs a ZrO 2 -doped nanostructured TiO 2 semiconductor to improve the photovoltage and an organic dye (TH305 [16] ) to harvest sunlight in the 400-750 nm region, giving an efficiency of 9.05 % with a high photovoltage (794 mV), while the back sub-cell employs a normal TiO 2 electrode sensitized with a different organic dye (HY103 [12] ) to capture sunlight in the 500-800 nm region, achieving an additional efficiency of 2.45 %. The overall energy conversion efficiency of this tandem DSC is 11.5 %.The two sub-cells are separated by a double-sided fluordoped tin oxide (FTO) conducting glass. Figure 1 shows pictures of the actual cell setup and a schematic of its construction. Shifting the CB band of TiO 2 towards more negative values is an effective way to improve the open-circuit photovoltage (V oc ) and increase the DSC's efficiency. There are two methods to make the CB more negative: adding an organic base to the electrolyte, and doping the TiO 2 with semiconductor materials with a more-negative CB energy level (E CB ). In our system, we added 4-tert-butylpyridine (TBP) to the electrolyte and also adopted the doping method by using ZrO 2 , which has a wider band gap (ca....

Solar cells sensitized with near-infrared absorbing dye: Problems with sunlight conversion efficiency revealed in ultrafast laser spectroscopy studies

“…The maximum available efficiency of such tandem configuration is 20%, much more than the current laboratory record for DSSC equal to 13% [11]. However, despite several attempts at different constructions of tandem DSSC [12][13][14][15][16][17][18][19][20], the obtained efficiencies are still lower than for a single DSSC. The main reason is poor performance of the long-wavelengths part in terms of low incident-photon to current efficiencies (IPCE).…”

Developments in and prospects for photocathodic and tandem dye-sensitized solar cells

“…First reported in 2004 [54,55], this architecture has been employed to realize 11.5% conversion efficiency using spectrally complimentary organic dyes [56]. These can be configured either in series or in parallel.…”

Rapid Double‐Dye‐Layer Coating for Dye‐Sensitized Solar Cells using a New Method

“…For example, the fabrication of working electrodes takes several hours, and current and voltage also critically depend on it. [12,13] Herein, we report a method that can solve those two problems at the same time. [8] Previous research shows that higher concentrations of dyes?…”

“…Further-more, recent research focuses on broadening solar spectrum absorption by multiple dye layers on working electrodes for performance improvement. [12,13] Herein, we report a method that can solve those two problems at the same time. The proposed solvent system for dye coating results in fast dye coating with less concerns of dye degradation even at high temperatures, and is convenient for preparing double dye-coating layers on the working electrode.…”