Structurally Simple and Easily Accessible Perylenes for Dye-Sensitized Solar Cells Applicable to Both 1 Sun and Dim-Light Environments

The need for low-cost and highly efficient dyes for dye-sensitized solar cells under both the sunlight and dim light environments is growing. We have devised <b>GJ</b>-series push–pull organic dyes which require only four synthesis steps. These dyes feature a linear molecular structure of donor–perylene–ethynylene–arylcarboxylic acid, where donor represents <i>N</i>,<i>N</i>-diarylamino group and arylcarboxylic groups represent benzoic, thienocarboxylic, 2-cyano-3-phenylacrylic, 2-cyano-3-thienoacrylic, and 4-benzo­[<i>c</i>]­[1,2,5]­thiadiazol-4-yl-benzoic groups. In this study, we demonstrated that a dye without tedious and time-consuming synthesis efforts can perform efficiently. Under the illumination of AM1.5G simulated sunlight, the benzothiadiazole-benzoic-containing <b>GJ-BP</b> dye shows the best power conversion efficiency (PCE) of 6.16% with <i>V</i>_OC of 0.70 V and <i>J</i>_SC of 11.88 mA cm^–2 using liquid iodide-based electrolyte. It also shows high performance in converting light of 6000 lx light intensity, that is, incident power of ca. 1.75 mW cm^–2, to power output of 0.28 mW cm^–2 which equals a PCE of 15.79%. Interestingly, the benzoic-containing dye <b>GJ-P</b> with a simple molecular structure has comparable performance in generating power output of 0.26 mW cm^–2 (PCE of 15.01%) under the same condition and is potentially viable toward future application

Application of Supramolecular Assembly of Porphyrin Dimers for Bulk Heterojunction Solar Cells

Recently, there has been a growing interest in developing porphyrin derivatives as electron donor materials in solution-processed organic solar cells. In contrast to the traditional synthesis route, we adopt a ligand-mediated supramolecular assembly approach to produce a new soluble porphyrin derivative. The complexation of nitrogen lone pairs in the bidentate ligands to the axial orbitals of both zinc atoms in zinc-metalated porphyrin dimers (KC2s) form KC2-duplex. The UV–vis absorbance of KC2-duplex displays a red-shift of the Q-band compared with that of KC2, indicating an improvement of intermolecular interaction. By blending KC2-duplex with [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the photoactive material for fabricating organic bulk heterojunction solar cells, the devices demonstrate a 38.7% enhancement of short-circuit current density (<i>J</i>_sc) as compared to those made from dimers. The largely enhanced <i>J</i>_sc is attributed to the improved charge transport dynamics of KC2-duplex:PC₇₁BM blend, including the hole and effective mobilities and exciton dissociation probability. When the photoactive film is processed from solvent containing 3% v/v 1-chloronaphthalene, <i>J</i>_sc is further enhanced (∼64.5%) as well as the fill factor (16.7%) for a power conversion efficiency of 3.06% from 1.63%. Our approach shown here can be generalized to other porphyrin-related systems to advance the development of porphyrin-based optoelectronic devices

Field-Induced Fluorescence Quenching and Enhancement of Porphyrin Sensitizers on TiO₂ Films and in PMMA Films

Three highly efficient porphyrin sensitizersYD2, YD2-oC8, and YD30, either sensitized on TiO₂ films or embedded in PMMA filmswere investigated using electrophotoluminescence (E-PL) spectra. Under both thin-film conditions, on application of an external electric field we observed the quenching of fluorescence of push–pull porphyrins (YD2 and YD2-oC8) and a slightly enhanced fluorescence of the reference porphyrin without an electron donor group (YD30). A nonfluorescent state with charge separation (CS) is proposed to be involved in both YD2 and YD2-oC8 systems so that the electron injection becomes accelerated in the presence of a strong electric field. In contrast, the retardation of the nonradiative process not involving a CS state was the reason for the field-induced enhancement of fluorescence of YD30. The extent of fluorescence quenching of YD2-oC8 was greater than that of YD2 on TiO₂ films, indicating that the <i>ortho</i>-substituted long alkoxyl chains play a key role to accelerate the consecutive electron injection involving the CS state. Our E-PL results indicate that a field-induced variation of fluorescent intensity is related to the efficiency of conversion of solar energy and that further improvement of the performance of devices containing push–pull porphyrin dyes is achievable under an applied electric field

Air-Stable Molecular Semiconducting Iodosalts for Solar Cell Applications: Cs₂SnI₆ as a Hole Conductor

We introduce a new class of molecular iodosalt compounds for application in next-generation solar cells. Unlike tin-based perovskite compounds CsSnI₃ and CH₃NH₃SnI₃, which have Sn in the 2+ oxidation state and must be handled in an inert atmosphere when fabricating solar cells, the Sn in the molecular iodosalt compounds is in the 4+ oxidation state, making them stable in air and moisture. As an example, we demonstrate that, using Cs₂SnI₆ as a hole transporter, we can successfully fabricate in air a solid-state dye-sensitized solar cell (DSSC) with a mesoporous TiO₂ film. Doping Cs₂SnI₆ with additives helps to reduce the internal device resistance, improving cell efficiency. In this way, a Z907 DSSC delivers 4.7% of energy conversion efficiency. By using a more efficient mixture of porphyrin dyes, an efficiency near 8% with photon confinement has been achieved. This represents a significant step toward the realization of low-cost, stable, lead-free, and environmentally benign next-generation solid-state solar cells

Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting

Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current–voltage (<i>I</i>–<i>V</i>) characteristics as an indicator to qualify the <i>I</i>–<i>V</i> sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications