Thogiti Suresh

Influence of thermal and solvent annealing on the morphology and photovoltaic performance of solution processed, D–A–D type small molecule-based bulk heterojunction solar cells

Four new solution-processable donor–acceptor–donor (D–A–D) structured organic small molecules (CSDPP9, CSDPP10, CSDPP11 and CSDPP12) with diketopyrrolopyrrole (DPP) as the central core unit and different electron donating groups as the terminal units, were designed and synthesized. These molecules employed as donors along with PC71BM as an electron acceptor in solution processed bulk heterojunction (BHJ) solar cells, exhibited a strong visible (450–650 nm) absorption band with suitable molecular orbital energy levels. OSCs based on these small molecules achieved moderate power conversion efficiency (PCE) in the range of 2.86–3.55% along with high open circuit voltage (Voc) and the difference is correlated with the different electron donating units used in the DPP. The observed high open circuit voltage (Voc) of the device is directly related to the HOMO energy level of the DPP. The BHJ devices, based on CSDPP11:PC71BM and CSDPP12:PC71BM subjected to solvent and thermal annealing showed improved PCEs of 5.47% and 4.88% respectively. The enhancement in the PCE has been attributed to the improved charge carrier mobility, crystallinity and light harvesting ability of the active layer.

High Molar Extinction Coefficient Ru(II)-Mixed Ligand Polypyridyl Complexes for Dye Sensitized Solar Cell Application

Two new ruthenium(II) mixed ligand terpyridine complexes, “Ru(Htcterpy)(NCS)(L1) (N(C4H9)4), mLBD1” and Ru(Htcterpy)(NCS)(L2)(N(C4H9)4), mLBD2 were synthesized and fully characterized by UV-Vis, emission, cyclic voltammogram, and other spectroscopic means, and the structures of the compounds are confirmed by 1H-NMR, ESI-MASS, and FT-IR spectroscopes. The influence of the substitution of L1 and L2 on solar-to-electrical energy conversion efficiency (η) of dye-sensitized solar cells (DSSCs) was evaluated relative to reference black dye. The dyes showed molar extinction coefficients of 17600 M−1 cm−1 for mLBD1 and 21300 M−1 cm−1 for mLBD2 both at λ maximum of 512 nm, while black dye has shown 8660 M−1 cm−1 at λ maximum of 615 nm. The monochromatic incident photon-to-collected electron conversion efficiencies of 60.71% and 75.89% were obtained for mLBD1 and mLBD2 dyes, respectively. The energy conversion efficiencies of mLBD1 and mLBD2 dyes are 3.15% (𝐽SC=11.86 mA/cm2, 𝑉OC=613 mV, ff=0.4337) and 3.36% (𝐽SC=12.71 mA/cm2, 𝑉OC=655 mV, ff=0.4042), respectively, measured at the AM1.5G conditions, the reference black dye-sensitized solar cell, fabricated and evaluated under identical conditions exhibited η-value of 2.69% (𝐽SC=10.95 mA/cm2, 𝑉OC=655 mV, ff=0.3750).

Substitution of Ethynyl-Thiophene Chromophores on Ruthenium Sensitizers: Influence on Thermal and Photovoltaic Performance of Dye-Sensitized Solar Cells

A new high molar extinction coefficient ruthenium(II) bipyridyl complex, “Ru(2,2-bipyridine-4,4′-dicarboxylic acid)(4,4′-bis((3-hexylthiophen-2-yl)ethynyl)-2,2′-bipyridine)(NCS)2 (N(C4H9)4), MC101” was synthesized and fully characterized by 1H-NMR, ESI-MASS, FT-IR, UV-Vis., and fluorescence spectroscopes. The dye showed relatively high molar extinction coefficient of 25.0 × 103 M-1 cm-1 at λ maximum of 544 nm, while the reference C101 has shown 15.8 × 103 M-1cm-1 at λ maximum 528 nm. The monochromatic incident photon-to-collected electron conversion efficiency of 44.1% was obtained for MC101 over the entire visible range, while the C101 sensitized solar cell fabricated and evaluated under identical conditions exhibited 40.1%. The DSSCs fabricated with 0.54 cm2 active area TiO2 electrodes and high efficient electrolyte (E01), from the sensitizers MC101 and C101 exhibited energy conversion efficiencies of 3.25% (short-circuit current density (JSC) = 7.32 mA/cm2, VOC = 610 mV, ff = 0.725) and 2.94% (JSC = 6.60 mA/cm2; VOC = 630 mV; ff = 0.709), respectively, under air mass of 1.5 sunlight.