Modified SnO₂ with Alkali Carbonates as Robust Electron-Transport Layers for Inverted Organic Solar Cells

Abstract

We report for the first time that alkali carbonates (Li 2 CO 3 , K 2 CO 3 , and Rb 2 CO 3 ) based on a low-temperature solution process can be used as interfacial modifiers for SnO 2 as robust electron-transport layers (ETL) for inverted organic solar cells (iOSCs). The room-temperature photoluminescence, the electron-only devices, and the impedance studies altogether suggested the interfacial properties of the alkali carbonates–modified SnO 2 ETLs, which were much better than those based on the SnO 2 only, provided efficient charge transport, and reduced the charge recombination rates for iOSCs. The iOSCs using the polymer donor poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b ;4,5- b ′]dithiophene-2,6-diyl- alt -(4-(2-ethylhexyl)-3-fluorothieno[3,4- b ]thiophene-)-2-carboxylate-2-6-diyl] and the fullerene acceptor phenyl-C 70 -butyric acid methyl ester as the active layer showed the average power-conversion efficiencies (PCEs) based on ten devices of 6.70, 6.85, and 7.35% with Li 2 CO 3 -, K 2 CO 3 -, and Rb 2 CO 3 -modified SnO 2 as ETLs, respectively; these are more than 22, 24, and 33% higher than those based on the SnO 2 only (5.49%). Moreover, these iOSC devices exhibited long-term stabilities, with over 90% PCEs remaining after the devices were stored in ambient air for 6 weeks without encapsulations. We believe that alkali carbonates–modified SnO 2 approaches are an effective way to achieve stable and highly efficient iOSCs and might also be suitable for other optoelectronic devices where an ETL is needed, such as perovskite solar cells or organic light-emitting diodes.

Self‐Assembled Monomolecular Layer Modified ZnO for Efficient Inverted Polymer Solar Cells with 11.53% Efficiency

“…Evidently, the RMS of the active layers coated on the ZnO‐APTES is smaller than that of the active layers on the pristine ZnO, indicating the excellent forming characteristics of the active layers on ZnO‐APTES. These results well match with the reducing R S of the inverted PSCs for performance improvement …”

Benzoselenadiazole‐core asymmetric D‐A‐A small molecule for solution processed bulk heterojunction organic solar cells

“…Apart from some excellent properties of PEDOT:PSS, there are some serious issues associated with PEDOT:PSS such as its acidic nature and the insulating characteristics of PSS which restricts the PEDOT:PSS conductivity 35 . Due to associated critical issues with PEDOT:PSS, researchers are working on exploring the possibilities of n‐type metal oxides ZnO (Zinc oxide), SnO 2 (Tin oxide) and TiO 2 (Titanium oxide) as buffer layers for the photovoltaic fabrication 36‐38 . For hybrid photovoltaics, TiO 2 is highly used electron transporting layer and also serves the purpose of an excellent buffer layer for OSCs due to its ultra‐thin film transparency, good chemical stability and high electrical conductivity 39 .…”

“…35 Due to associated critical issues with PEDOT: PSS, researchers are working on exploring the possibilities of n-type metal oxides ZnO (Zinc oxide), SnO 2 (Tin oxide) and TiO 2 (Titanium oxide) as buffer layers for the photovoltaic fabrication. [36][37][38] For hybrid photovoltaics, TiO 2 is highly used electron transporting layer and also serves the purpose of an excellent buffer layer for OSCs due to its ultra-thin film transparency, good chemical stability and high electrical conductivity. 39 The excellent electron extraction and the charge transport capabilities of TiO 2 make it a superior alternative to PEDOT:PSS which lowers the recombination possibilities and improves the electron mobility.…”

Enhanced dissociation of excitons and charge transfer in organic solar cells of polymer:fullerene blends with molecular BPFZn doping

“…We studied the molecularly doped OSCs based on a polymer:fullerene blend in an inverted structure (Figure 1a, b). The electronic energy levels of the components, BPFZn, 23 MoO 3, 26 and all others 27 are taken from the literature and displayed in Figure 1c. We analyzed the UV‐Vis‐NIR absorption spectra of a p‐type donor (PTB7‐Th), a fullerene acceptor (PC 71 BM), and a dopant (BPFZn) in a solution (Figure 1d).…”