Novel indole-based photosensitizers coupled with PEG-HEC quasi-solid-state electrolyte to improve energy conversion and stability of organic dyes based-dye sensitized solar cells

•First report on the effect of organic dye combination with PEG-HEC QSSE.•Molar absorption coefficient and energy level varied by the terminal acceptor group in organic dye.•Suppression in recombination reaction which enhance PCE to 6.2% for DTTCY dye.•Improved the stability of DSSCs by the role of quasi-solid state electrolyte. A series of novel Indole based organic dyes were synthesized and coupled with a Poly-ethylene glycol-Hydroxy ethyl cellulose quasi-solid-state-electrolyte (PEG-HEC QSSE) polymer blended iodine electrolyte to obtain a metal-free dye-based dye-sensitized solar cell (DSSCs) with better stability. The newly synthesized organic dyes were confirmed through 1H, 13C NMR, CHN analysis. The optical and electrochemical properties of the dyes were determined using UV-visible spectrometry and cyclic voltammetry techniques. A quasi-solid state (QSS) blended polymer PEG-HEC with iodide redox couple as electrolyte was characterized via Field emission Scanning Electron microscope (FE-SEM), UV-visible spectroscopy, XRD and DSC. A foremost comparative study was analysed on DSSC devices with the newly synthesised organic dyes (DPC, DTC, DPCY, DTCY, DPTCY and DTTCY) coupled with the QSSE. The electrochemical impedance spectrum was discussed for all the six dyes coupled with PEG-HEC QSSE, among that DTTCY sensitized device exhibits good ionic conductivity (1.13 × 10−3 S cm−1), high chemical capacitance (Cµ=17.01 µF), high recombination resistance (53.97 Ω) and lower charge transfer resistance (2.35 Ω) due to the presence of a strong electron-withdrawing group in the organic dye and also QSS behaviour of electrolyte. The longer electron lifetime (τn-58.51 ms) and better diffusion coefficient (4.25 × 10−7 cm2 s−1) of the device prove the short circuit current (Jsc= 16.39 mA cm−2) and enhancement of power conversion efficiency (PCE) of 6.24 % with better stability under AM 1.5 G illumination (100 mW cm−2). The combination of new Indole based organic dyes with PEG-HEC QSSE paved a way to improve the PCE and stability of organic dyes based DSSCs. [Display omitted]