An Organic D-π-A Dye for Record Efficiency Solid-State Sensitized Heterojunction Solar Cells

Abstract

D ye-sensitized solar cells (DSCs) have attracted significant attention as low-cost alternatives to conventional semiconductor photovoltaic devices. 1,2 These cells are composed of a nanocrystalline wide band gap semiconductor oxide, e.g., TiO 2 deposited on a transparent conducting oxide (TCO) glass substrate. A molecular sensitizer is linked via an anchoring group to the oxide surface. Upon light excitation, it injects an electron into the conduction band of the semiconductor. Ruthenium complexes as molecular sensitizers have shown impressive solarto-electric power conversion efficiencies (PCE) in liquid electrolyte based devices, with the PCE reaching over 11% under standard AM1.5G full sunlight. [3][4][5][6][7] Recently, metal-free organic dyes have attracted increasing attention due to their high structural flexibility, high molar extinction coefficient, low toxicity, and environmental friendliness. DSCs employing organic dyes featuring an electron donor and acceptor moiety connected by a π-conjugation bridge have reached ∼10% efficiency with liquid electrolytes. [8][9][10][11][12] They can be easily modified to tune their properties for device performance optimization. One of the main factors limiting the performance of DSCs with organic dyes is the formation of dye aggregates on the surface of the semiconductor oxide, leading to quenching of the excited state of the dye molecules and lowering the overall performance of the device. 13 Appropriate molecular structural modifications have been conceived to avoid this undesirable aggregation process. [14][15][16] In solid-state DSCs (ssDSCs) a solid hole-transporting material (HTM) is employed to replace the liquid redox electrolyte which is responsible for the dye regeneration and hole transfer to the counter electrode. Typically, solid HTMs have shorter charge carrier diffusion lengths than liquid redox electrolytes. Due to incomplete pore filling of thicker TiO 2 films with solid HTMs, the ssDSCs are restricted to using thinner titania films. High molar extinction coefficient dyes are of great importance for this type of device in order to enable the use of thinner films. On the basis of this strategy, we have designed and synthesized the 4, 4 0 -didodecyl-4H-cyclopenta[2,1-b:3,4-b 0 ]dithiophene (CPDT) segment which is used as the spacer between the donor and the acceptor group of a metal-free organic sensitizer (called C220).Here, we report on the photovoltaic performance of the C220 sensitizer in a ssDSC using spiro-MeOTAD as the organic holetransporting material.The molecular structure of the C220 dye is presented in Figure 1, which is analogous to the recently reported C218 dye except that dodecyl substituents replace the two hexyl substituents on the CPDT segment. 17 The detailed synthesis of C220 is described in the Supporting Information. The electronic Received: November 18, 2010 Revised: February 7, 2011 ABSTRACT: The high molar absorption coefficient organic D-π-A dye C220 exhibits more than 6% certified electric power conversion efficiency at ...

Hole Transport and Recombination in All-Solid Sb2S3-Sensitized TiO2 Solar Cells Using CuSCN As Hole Transporter

“…The completed cells, which were not sealed, were stored, transferred, and measured in a dry air atmosphere (synthetic air (20% O 2 À80% N 2 ) from a cylinder). Because of the important effect caused by the initial light soaking and the choice of the gas atmosphere in contact with the cell, 14 an initial light soaking treatment was carried out for 2 h. During this initial treatment as well as in the subsequent electrical characterization the cells were placed in a special sealed metal holder, allowing us to keep the cells under a small dry air (synthetic air) flow atmosphere, while also providing the electrical contacts, a cell temperature control system, and the masked windows to have a constant active surface of 0.54 cm 2 . During the initial like soaking treatment, the cells were placed under 1 sun illumination at 40°C under dry air flow at open circuit, while collecting currentÀpotential (JÀV) scans every 10 min.…”

Characterization of intrinsic hole transport in single-crystal spiro-OMeTAD

“…These advantages make spiro-OMeTAD the most extensively studied organic HTM for hybrid organic-inorganic solar cells with high power conversion efficiency. [5][6][7][8] However, as it is the role of the molecular spiro center to make crystallization difficult, spiro-OMeTAD films are usually amorphous, which results in very low hole mobilities and necessitates doping the materials to improve hole conductivity. This leads to a serious issue limiting the reproducibility and performance of the photovoltaic devices.…”

The Effect of Hole Transport Material Pore Filling on Photovoltaic Performance in Solid‐State Dye‐Sensitized Solar Cells

“…State-of-the-art ss-DSCs using fi lms of mesoporous TiO 2 and spiro-OMeTAD as a HTM have just recently reached 6% effi ciency [ 8 ] and are optimized at a fi lm thickness of 2 μ m. Cells built with thicker fi lms absorb more light but exhibit poor charge collection. This has been attributed to short diffusion lengths of charge carriers inside the cell at operating voltages [ 9 ] , [ 10 ] and to the incomplete fi lling of TiO 2 pores with spiro-OMeTAD.…”