Synthesis of Two-Dimensional Polythiophenes Comprising Conjugated Pendants for Polymer Solar Cells

Autor: Hsing-Ju Wang, 王杏如
Rok vydání: 2012
Druh dokumentu: 學位論文 ; thesis
Popis: 100
Conjugated polythiphenes (PTs) have attracted significant scientific interest recently as their electronic and opto-electronic properties can be manipulated through intramolecular charge transfer (ICT). Such polymers may have potential in novel materials for polymer solar cell applications. Instead of typical linear conjugated polymers, we designed and synthesized two-dimensional (2D) PTs comprising conjugated pendants, adopting the side chain type ICT to modulate the properties and photovoltaic (PV) performance in this study. Herein, we summarized the systematic studies on some topics. First, we studied the bulky side chain density effect on 2D PTs, and then compared the properties between linear conjugated polymers and 2D PTs with conjugated pendants. Moreover, the influences of various electron donor/acceptor conjugated pendants on the photophysical, electrochemical and PV properties of 2D PTs were also addressed. The details of each topic are summarized as below: 1. Bulky side chain density effect on 2D PTs: 2D PTs with regioregular (rr) and random (r) configurations of PTs, namely rr-TPATh-PT, r-CzPh-PT, and r-TPATh-PT, featuring triphenylamine (TPA) and carbazole (Cz) as pendants along with thiophene (Th) and phenyl (Ph) to extend the conjugated length of the pendants were synthesized in this study. Due to the steric hindrance of bulky pendants, the effective conjugation length of 2D PTs could be curtailed, and consequently the HOMO energy level was lowered. Moreover, r-TPATh-PT with less bulky side-chain content provided sufficient free volume for PC61BM intercalation. Better compatibility was observed for the r-TPATh-PT/PC61BM-blend film as compared to the rr-TPATh-PT/PC61BM-blend film. After an annealed treatment, the PSC fabricated from the blend of r-TPATh-PT and fullerene derivative PC71BM (w/w =1:3), with a short-circuit current (Jsc) of 6.83 mA/cm2, Voc of 0.71 V and a power conversion efficiency (PCE) of 1.75 %. 2. 2D PTs with TPA pendants: In this part of study we synthesized three 2D PTs, namely PTBPTPA, PTStTPA, and PTCNStTPA, featuring three different conjugated units, biphenyl (BP), stilbene (St), and cyanostilbene (CNSt), respectively, in the polymer backbones, and conjugated triphenylamine/thiophene (TPATh) moieties on the side chains. In addition, we also synthesized three conjugated BP-, St-, and CNSt-based main-chain type conjugated polymers (PTBP, PTSt, and PTCNSt, respectively). The twisting of the main chain out of planar-conjugation in the presence of bulky moieties could be suppressed though the incorporation of rigid conjugation units (BP, St, CNSt) onto the backbone. Thereby high degrees of ICT were induced within the conjugated frameworks of the polymers, resulting in lower band gap energies and red-shift of the maximal UV–Vis absorption wavelengths. The photovoltaic performances of PSCs fabricated from blends of the 2-D PTs/PC61BM were superior to those of PSCs based on the main-chaintype polymer/PC61BM blends. The PTBPTPA/PC61BM (w/w=1:1) blend based PSC exhibited the highest Jsc (1.38 mA/cm2) and PCE (0.38%). 3. 2D-PTs with TPA and Cz: In this part of study we synthesized four 2D-PTs, namely PTtTPA, PBTtTPA, PTtCz and PBTtCz, featuring two different unsubstituted moieties—thiophene (T) and bithiophene (BT) —in the polymer backbones, and conjugated moieties, TPA and Cz each with a tert-butyl group on the side chain (tTPA and tCz, respectively). Due to the stronger donor strength of tTPA than that of tCz pendants, the improved electron transfer between polymer chains resulted in broader absorption spectra and lower energy band gaps of 2D-PTs. In addition to the higher oxidation potential of tCz than that of tTPA based 2D-PTs, lower HOMO levels of the studied PTtCz and PBTtCz were obtained. The highest PSC performance of PBTtTPA/PC61BM (w/w=1:1) blend based device reached PCE of 1.94 %. 4. 2D-PTs with dibenzo[d]thiazol-2-ylmethane (DBT) or malononitrile (DCN) pendants: In this part of study, we synthesized fluorene (F)/thiophene (T)-based conjugated polymers (PFTs), namely PFDBT, PFDBTBT and PFDCNBT, featuring unsubstituted moieties, BT in the polymer backbones, andconjugated moieties, DBT and DCN on the side chains. With longer BT conjugated moieties incorporated onto the main chains of 2D PFTs, we were able to increase planarity of polymer backbone and lower the energy band gaps. Due to the better planar structure of DBT pendants than that of DCN, the ICT effect resulting in lower energy band gap was observed for PFTs comprising DBT pendants. The best performance of photovoltaic device was obtained using PFDBTBT/PC61BM blend (w/w=1:1) as photo-energy conversion layer (PCE=0.73 %). These 2D conjugated polymers presented better PV performance than the main chain conjugated polymers. The desirable PV performance can be achieved by adjusting side chain density and incorporating suitable donor/acceptor conjugated pendants.
Databáze: Networked Digital Library of Theses & Dissertations
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