Self-Assembled Monolayers (SAMs)
Self-assembled monolayers (SAMs) are well-organized, ultra-thin layers that form on a substrate's surface through either weak physical forces or strong chemical covalent bonds. They are described as monolayer as they are one molecule thick layers. Molecular self assembly refers to the process where these molecules spontaneously organize into precise, functional self-assembled structures. The formation of SAMs typically involves deposition and thermal annealing.
The natural tendency of certain molecules to form organized patterns through non-covalent interactions can be exploited for electronic devices. Organic molecules can self-assemble into conductive or semiconductive materials, which are used in organic light-emitting diodes (OLEDs), organic photovoltaic cells, and organic field-effect transistors (OFETs). SAMs can act as an interface, i.e. hole injection monolayer (HIML) between the electrode and the active layer materials in optoelectronic devices.
Serving as hole selective contact layer and alternative to PEDOT:PSS, SAMs improve the device performance of dye-sensitized solar cells, organic solar cells, and inverted perovskite or polymer solar cells. The following are examples of solar cells device performance engaging different SAM molecules as hole transport layers:
Device Structure | VOC (V) | JSC (mA/cm2) | FF (%) | PCE (%) |
ITO/2PACz/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/C60/BCP/Cu | 1.158 | 21.7 | 80.91 | 20.26 |
ITO/Br-2PACz/Cs0.25FA0.75Sn0.5Pb0.5I3/C60/BCP/Ag | 0.81 | 32.14 | 74.94 | 19.51 |
ITO/MeO-2PACz/MA0.05FA0.95Pb(I0.95Br0.05)3/C60/BCP/Cu | 1.12 | 23.5 | 80.6 | 21.2 |
ITO/MPA-CPA/perovskite/C60/BCP/Ag | 1.20 | 24.8 | 84.5 | 25.2 |
ITO/perovskite (DMAcPA doping)/PC60BM/BCP/Ag | 1.187 | 25.69 | 84.73 | 25.86 |
ITO/4PADCB(CbzNaph)/FA0.8Cs0.2Pb(I0.6Br0.4)3/C60/SnO2/IZO/PEDOT:PSS/FA0.6MA0.3 Cs0.1Sn0.5Pb0.5I3/C60/SnO2/Cu | 2.12 | 15.19 | 82.6 | 26.6 |
Our collection of self-assembled monolayers includes molecules with electron rich carbazole, 9,9-dimethylacridine, 7H-dibenzo[c,g]carbazole, or triphenylamine terminal functional groups, alkyl or cyano-vinyl linkers, and phosphonic or carboxylic acid anchoring groups.
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