Liquid eutectic GaIn as an alternative electrode for PTB7:PCBM organic solar cells

Abstract

Conventional vacuum deposition process of aluminum (Al) is costly, time-consuming and difficult to apply to the large-scale production of organic photovoltaic devices (OPV). This paper reports a vacuum-free fabrication process of poly[[4,8-bis(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thienophenediyl]:[6,6]-phenyl C71 butyric acid methyl ester (PTB7:PCBM) bulk heterojunction organic solar cell with liquid eutectic gallium–indium (EGaIn) electrode as an alternative to the common Al electrode. The insertion of a thin poly(ethylene oxide) (PEO) layer after depositing organic photoactive layer could help prevent the diffusion of liquid EGaIn into the active layer and allow the deposition of the EGaIn electrode. The PEO interfacial layer was formed by spin-coating from a mixed solvent of alcohol and water. Among different alcohol+water (methanol, ethanol, ethylene glycol, n-propanol, isopropanol, and isobutanol) mixed solvent tested, the n-propanol+water mixed solvent showed the greatest enhancement to the performance of OPVs. The improved device performance was attributed to the reactivity of mixed solvent n-propanol+water toward the surface of PTB7:PCBM active layer, which could help optimize surface morphology.

Blade Coating of Alloy as Top Electrodes for Efficient All‐Printed Organic Photovoltaics

“…LMPAs have been used as top electrodes in optoelectronic devices, such as organic light-emitting diode, [31] quantum-dot light emitting diodes, [32][33][34] perovskite light-emitting diode, [29] and perovskite solar cells, [35,36] For OPVs, the attempts of LMPA-electrodes mainly focused on the EGaIn, which is a liquid at the room temperature due to its low melting point of 15.7 °C. [37][38][39][40][41] The liquid phase EGaIn is easy to be spray deposited, but the devices are vulnerable to even very light touches. LMPAs with melting points between 60 and 80 °C are appropriate choices for OPVs because the electrodes should remain solid under heating by solar irradiations while the processing temperature should be <80 °C to avoid harming the photoactive layer.…”

“…[49] But blade coating is rarely used to print the top electrode of OPVs. [39,48] In this work, blade coating of FM as the top electrode of the non-fullerene-acceptor OPV is investigated. In conventional blade coatings, the blade is rigid and the liquid alloy tends to reflow from the blade-substrate gap to form a film that is excessively thick for the top electrode due to the high surface tension (≈600 mN m −1 ).…”

Improvement of Vacuum Free Hybrid Photovoltaic Performance Based on a Well-Aligned ZnO Nanorod and WO3 as a Carrier Transport Layer

“…Eutectic gallium–Indium alloy has been applied as a cathode in the hybrid PVs configuration [23,24]. This alloy exists in the liquid phase at room temperature, has a melting point of ~15.5 °C, and is non-toxic.…”

Fabrication and optimization of vacuum free hybrid solar cells prepared using composites of zinc oxide nanoparticles and narrow band gap polymer composite

“…Eutectic gallium-indium (EGaIn) alloy has been used as a cathode in the BHJ solar cell configuration. 12,13) This alloy exists in the liquid phase at room temperature, has a melting point of ∼15.5 °C, and is non-toxic. It also has high electrical conductivity (∼3.4 × 10 4 S cm −1 ) similar to Al (∼3.5 × 10 4 S cm −1 ), and a work function of EGaIn (∼4.2 eV) is very close to that of Al (∼4.3 eV), and can be deposited simply at room temperature without the need for a thermal evaporator system or specialized equipment.…”