Functionalized Thermoplastic Polyurethane as Hole Conductor for Quantum Dot-Sensitized Solar Cell

Abstract

A hole conducting layer for quantum dot sensitized solar cell (QDSS) as a function of redox behavior has been reported. Polyurethanes, comprising hard and soft segments, have been functionalized for its use in solar cell application. Functionalization has been confirmed through NMR and FTIR studies. The functionalization of hard segment results in incorporation of ionic moieties which enhances its electrical conductivity, electrochemical and optical properties and displays a crucial role as a hole transport materials for QDSS cells due to proper work function and reduces energy barrier at the interface of active layer and counter electrode leading to reversible charge transport without decomposition. Cadmium sulfide (CdS) quantum dot has been synthesized using capping agent and the size (4 nm) and shape (spherical) has been confirmed through various techniques, including TEM, AFM, SEM, and DLS. Energy diagram of whole system has been revealed by measuring HOMO-LUMO and VB-CB energy gap through cyclic voltammetry and UV-vis spectrophotometry. The proper energy level alignment with electron transport layer and electron collecting layer provides suitability to transport hole for continuous harvesting of light. Solar cell device has been fabricated using successful layered design of functionalized polyurethane. The incorporation of a thin polyaniline (PANi) layer helps reducing the electron transport toward reverse direction (cathode) by adjusting the LUMO energy gap of polymer gel electrolyte and confirms re-excitation of dropped electron toward quantum dots (photoanode) through quenching under continuous illumination. The device with structure FTO/TiO2/CdS/PANi/PGE/Pt exhibits a photocurrent density of (Jsc ∼ 2.20 mA/cm2), open circuit voltage Voc of 0.60 V, fill factor of 0.78 and photovoltaic conversion efficiency (PCE) of 1.25% using functionalized polyurethane. Copyright © 2018 American Chemical Society.