Semi-crystalline photovoltaic polymers with efficiency exceeding 9% in a ∼300 nm thick conventional single-cell device

Abstract

New semi-crystalline photovoltaic polymers were synthesized and the optimized device exhibited 9.39% efficiency in a ∼300 nm thick single-cell device.

Impact of Backbone Fluorination on π-Conjugated Polymers in Organic Photovoltaic Devices: A Review

“…In a different work, Woo et al investigated the fluorination of benzothiadiazole in a D/A copolymer including thiophene-dialkoxybenzene-thiophene as an electron-donor comonomer [70,81]. The authors could demonstrate, through the investigation of three different polymers (non-fluorinated PPDTBT, mono-PPDTFBT and di-fluorinated PPDT2FBT copolymers, see Figure 10), that the SCLC mobility increased with the fluorine substitution for both electrons and holes.…”

“…A dominantly parallel orientation of the lamellae along the substrate therefore hinders out-of-plane charge transport and leads to poor charge collection [75]. One of the most striking and, presumably, the most effectual consequence of fluorination appears to be the frequently observed presence of perpendicularly oriented lamellae [28,32,69,70,72]. The corresponding out-of-plane orientation of the π-π stacking direction leads to a high out-of-plane hole mobility, which opens the route towards thicker active layers without loss in fill factor.…”

“…The higher out-of-plane hole mobility was shown to contribute most to these improved photovoltaic performances. Similarly, Woo et al [70] reported reduced π-π stacking distances upon fluorination of PPDTBT (see Figure 10), with a pronounced impact on the charge transport in thick active layers (up to 1 µm thick) and thus on the photovoltaic device performances (see Entry 2, Table 4). Moreover, in their investigation, a computational study led them to attribute both the higher backbone planarity and the more intense interchain packing to F ... H and F ... S interactions.…”

“…A number of recent reports have shown that fluorination of conjugated polymer backbones can have a strong impact on one or several of these properties, often leading to a more favorable morphology and to improved photovoltaic performances. Adding fluorine heteroatoms has, for instance, been found to enhance the domain purity (lowering the charge carrier recombination rate) [25,59,67], reduce the domain size [28,32,59,67], enhance the structural order [24,25,28,29,59,61,[69][70][71] and promote polymer face-on orientation at the interface with the bottom electrode [28,32,59,61,67,69,72] (increasing the out-of-plane hole mobility) or induce a face-on orientation at the D/A interface [69,73]. However, these effects can be more or less pronounced or even reversed [27,33,67], depending on the molecular structure of the conjugated building blocks as well as on the nature and positioning of the solubilizing side-chains.…”

Thiophene and Naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole Based Alternating Copolymers for Polymer Solar Cells

“…Currently, great advances have been made in organic photovoltaics (OPVs) by development of semi-crystalline low band gap donor-acceptor (D-A) polymers with broad light absorption and high carrier mobility [1][2][3][4]. Fullerene based polymer solar cells (PSCs) already achieved the power conversion efficiencies (PCEs) over ~9-11% [5][6][7][8][9][10]. Given the various photovoltaic polymers reported during the last decade, benzothiadiazole (BT), mono-and difluroinated BT (FBT, 2FBT) have been widely studied and proven to be one of the most promising electron-withdrawing building block to yield D-A type high-performance PSCs [7,8,11].…”