Stabilizing polymer-based bulk heterojunction solar cells via crosslinking

Abstract

cited By 42International audienceReviewed are crosslinking strategies to stabilize the active-layer morphology of organic solar cells, namely donor-to-donor, donor-to-acceptor and acceptor-to-acceptor. The active layer of a polymer photovoltaic cell is mainly based on a blend of two components: a semiconducting polymer (electron donor) and a fullerene derivative (electron acceptor) to form the bulk heterojunction (BHJ). To offer optimum photovoltaic performances, the morphology of this layer has to be very carefully controlled at the nanoscale. The materials of the BHJ require specific phase segregation enabling the optimum photogenerated exciton diffusion and dissociation, and also to ensure pathways for charge carriers to electrodes. However, such a specific morphology is thermodynamically unstable over time and phase segregation occurs with thermal cycling under solar operating conditions inducing a decrease of solar cell efficiency. This review reports on the recent progress towards obtaining a stable optimized BHJ morphology and improved efficiency stability, using different chemical routes for crosslinking the organic semiconductors. © 2014 Society of Chemical Industry

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

“…Several techniques have been developed over the last decade to improve the thermal stability of polymer:fullerene blends including the use of high glass transition temperature polymers, [14] ternary blends with compatibilizers such as block copolymers, [15][16][17] amorphous fullerene derivatives, [18,19] donor-acceptor systems with enhanced interactions, [20,21] functionalized side chains on the polymer, [22] thermocleavable polymers, [23] light-induced fullerene polymerization, [24,25] and cross-linkable materials. [26,27] Furthermore, it was shown that mixtures of different fullerenes can improve the thermal stability of BHJs. [28][29][30][31][32] Despite an intense research, known techniques to stabilize BHJs either reduce only partially thermal degradation or produce poor device efficiencies.…”

Crosslinked Semiconductor Polymers for Photovoltaic Applications

“…In addition to the crosslinking of donor polymers, crosslinkable fullerene derivatives were also investigated in the last years and are discussed in the reviews of Wantz et al and Rumer et al [14] …”

“…This is among the highest PCEs reported for OPVs using crosslinked active layers. [34] In the context of oxetane functionalization, it is noteworthy that, although it is generally assumed that this mechanism requires the exposure to an acid, [14,35] Knauer et al [15] showed that crosslinking via oxetane groups can be achieved by prolonged heating, yielding a fully crosslinked and long-term stable BHJ cell.…”

“…In a short review, however, it is not possible to cover all the work on crosslinked OSCs. [14] Instead, we decided to highlight work that leads to efficient OSCs or that we believe is important for the understanding and the development of crosslinked solar cells. We begin with work on the stabilization of BHJ solar cells followed by a section on the use of crosslinked layers and multilayer OSCs and end with a short section on patterning.…”

“…Crosslinking of the donor is often used, as it is relatively easy and versatile and may be applied to a variety of material classes. [14,18,22,25] In an attempt to systematically assess the relation between different functional groups and the stability of the crosslinked OSCs, comparative studies were performed by several groups. [22,25,32] Krebs and co-workers [22] compared bromine-, azide-, vinyl-, and oxetane-functionalized derivatives of the low bandgap polymer TQ1 (Figure 2).…”