Enhanced Performance of I₂‐Free Solid‐State Dye‐Sensitized Solar Cells with Conductive Polymer up to 6.8%

Abstract

An iodine‐free solid‐state dye‐sensitized solar cell (ssDSSC) is reported here, with 6.8% energy conversion efficiency—one of the highest yet reported for N719 dye—as a result of enhanced light harvesting from the increased transmittance of an organized mesoporous TiO2 interfacial layer and the good hole conductivity of the solid‐state‐polymerized material. The organized mesoporous TiO2 (OM‐TiO2) interfacial layer is prepared on large‐area substrates by a sol‐gel process, and is confirmed by scanning electron microscopy (SEM) and grazing incidence small‐angle X‐ray scattering (GISAXS). A 550‐nm‐thick OM‐TiO2 film coated on fluorine‐doped tin oxide (FTO) glass is highly transparent, resulting in transmittance increases of 8 and 4% compared to those of the bare FTO and conventional compact TiO2 film on FTO, respectively. The high cell performance is achieved through careful control of the electrode/hole transport material (HTM) and nanocrystalline TiO2/conductive glass interfaces, which affect the interfacial resistance of the cell. Furthermore, the transparent OM‐TiO2 film, with its high porosity and good connectivity, exhibits improved cell performance due to increased transmittance in the visible light region, decreased interfacial resistance (Ω), and enhanced electron lifetime (τ). The cell performance also depends on the conductivity of HTMs, which indicates that both highly conductive HTM and the transparent OM‐TiO2 film interface are crucial for obtaining high‐energy conversion efficiencies in I2‐free ssDSSCs.

Review—Single-Walled Carbon Nanohorn-Based Dye-Sensitized Solar Cells

“…[114][115][116][117] For example, Ahn et al synthesized novel honeycomb-like organized TiO 2 -based photoanodes as a means to increase the dye loading, light-scattering, and electrolyte wetting properties. 115 The graft copolymer poly(vinyl chloride)-gpoly(oxyethylene methacrylate) (PVC-g-POEM) and TiO 2 nanoparticles were directly mixed in a one-step synthesis forming selfassembled and hydrophilic TiO 2 nanocrystals.…”

Multi-layering of a nanopatterned TiO2 layer for highly efficient solid-state solar cells

“…Next, a solution containing 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) was Multi-layering of a Nanopatterned TiO 2 Layer J Na et al directly dropped onto the dye-adsorbed TiO 2 photoanode, followed by a solid-state polymerization 11,22,23 at 60°C to produce the conductive polymer, PEDOT as a HTM, to prepare an I 2 -free ssDSSC.…”

“…Among the various solar cells, iodine-free solid-state dye-sensitized solar cells (ssDSSCs) based on a conductive polymer as hole transporting materials have been attracting much interest recently owing to their low toxicity, light overall weight, long-term durability and processibility. 11,22,23 However, the photoconversion efficiency of ssDSSCs is low due to the wasted light that is transmitted through the photoanode. In our previous work, we introduced a nanopatterned TiO 2 photoanode, showing 40% and 33% enhancements of the short-circuit current (J sc ) and power conversion efficiency (PCE), respectively, compared with a flat TiO 2 photoanode in ssDSSCs.…”

Recent advances in small molecular, non-polymeric organic hole transporting materials for solid-state DSSC

“…Nevertheless, polymers cast from solutions must penetrate into the pores of the nanoparticles and should form a good contact with the adsorbed sensitizer. Semiconducting polymer as poly(3,4-ethylenedioxythiophene) (PEDOT) [18,19] and poly(3-hexylthiophene) (P3HT) [20] are mainly used in solid state DSSC as solid hole conductor [21]. However, the conversion efficiencies reported with conducting polymers as HTM are lower in comparison to the cells using a liquid electrolyte or small organic hole conductor molecules, mainly due to the incomplete filling of the TiO 2 nanopores by the HTM [22], which leads to poor electronic contact between the dye molecules and the hole conductor.…”

“…To overcome this drawback, in situ polymerized HTMs have been developed. The polymerization of monomers has taken place directly inside the TiO 2 networks leading to high efficient solid state DSSCs with η ranges from ∼4-7% [18,19,[23][24][25][26]. A breakthrough was recently reported in solid-state hybrid solar cells by using organolead iodide perovskite (CH 3 NH 3 PbI 3 ) nanoparticles [27] as a light absorber and spiro-MeOTAD as HTM, which shows an impressive PCE of 9.7% with superior stability over 500 h. Etgar et al [28] have described the photovoltaic device comprised of a mesoscopic CH 3 NH 3 PbI 3 /TiO 2 heterojunction with CH 3 NH 3 PbI 3 nanoparticles as both a light harvester and a HTM, which shows a high efficiency of 5.5% under 1 Sun illumination.…”