Size-Tuning of WSe₂ Flakes for High Efficiency Inverted Organic Solar Cells

Abstract

The development of large-scale production methods of two-dimensional (2D) crystals, with on-demand control of the area and thickness, is mandatory to fulfill the potential applications of such materials for photovoltaics. Inverted bulk heterojunction (BHJ) organic solar cell (OSC), which exploits a polymer-fullerene binary blend as the active material, is one potentially important application area for 2D crystals. A large ongoing effort is indeed currently devoted to the introduction of 2D crystals in the binary blend to improve the charge transport properties. While it is expected that the nanoscale domains size of the different components of the blend will significantly impact the performance of the OSC, to date, there is no evidence of quantitative information on the interplay between 2D crystals and fullerene domains size. Here, we demonstrate that by matching the size of WSe few-layer 2D crystals, produced by liquid-phase exfoliation, with that of the PCBM fullerene domain in BHJ OSCs, we obtain power conversion efficiencies (PCEs) of ∼9.3%, reaching a 15% improvement with respect to standard binary devices (PCE = 8.10%), i.e., without the addition of WSe flakes. This is the highest ever reported PCE for 2D material-based OSCs, obtained thanks to the enhanced exciton generation and exciton dissociation at the WSe-fullerene interface and also electron extraction to the back metal contact as a consequence of a balanced charge carriers mobility. These results push forward the implementation of transition-metal dichalcogenides to boost the performance of BHJ OSCs.

Building an Organic Solar Cell: Fundamental Procedures for Device Fabrication

“…The entire experiment took place over a three-day course [17,18] as depicted in the flow chart below in Figure 2.…”

Graphene-Based Hole-Selective Layers for High-Efficiency, Solution-Processed, Large-Area, Flexible, Hydrogen-Evolving Organic Photocathodes

“…[132][133][134] The latter can then be deposited on different substrates by established printing/coating techniques So far, the durability of the graphene/TMDs-based photocathodes has been tested over no more than 1 hourperiod 80,84 and further investigations on these classes of 2D materials as CSLs for PEC application are needed. In fact, despite both graphene derivatives and TMD flakes have been demonstrated as efficient HSL and ESL in solution-processed PVs, including organic, [148][149][150][151][152][153][154] dye sensitized, 155,156 and perovskite solar cells, [157][158][159][160][161] no endurance tests have been reported for graphene/TDMs-based photocathodes.…”

Poly(methyl methacrylate)‐Assisted Exfoliation of Graphite and Its Use in Acrylonitrile‐Butadiene‐Styrene Composites

“…The buoyant force F b = − ms ω 2 r , in which ms is the mass of the displaced solvent, and the frictional force F f =‐fσ , which depends on the friction coefficient between the solvent and the particle ( f ) and the sedimentation velocity of the particle itself ( σ ) . The sedimentation coefficient is defined as in Equation : …”

“…in which the ρ of the solvent and the particle are expressed as ρ s and ρ p , respectively. Thick and large flakes possess higher sedimentation coefficients compared to the small flakes, thus having a fast sedimentation . It is possible to prepare dispersions containing flakes with different lateral size, by changing the parameters of the centrifugation …”