Roll to roll compatible fabrication of inverted organic solar cells with a self-organized charge selective cathode interfacial layer

Abstract

We successfully demonstrate a simple approach to printing efficient, inverted organic solar cells (OSCs) with a self-organized charge selective cathode interface layer based on the small-molecule Phen-NaDPO.Different from previous studies, Phen-NaDPO molecules were blended into a polymer/fullerene blend, comprising a low bandgap diketopyrrolopyrrole-quinquethiophene alternating copolymer pDPP5T-2 and phenyl-C 61 -butyric acid methyl ester (PC 61 BM), and processed by doctor blading in air. We observed a spontaneous, surface energy driven migration of Phen-NaDPO towards the ZnO interface and a subsequent formation of electron selective and barrier free extraction contacts. In the presence of 0.5 wt% Phen-NaDPO, a PCE of 5.4% was achieved for the inverted device based on an ITO/ZnO cathode. Notably, the photovoltaic performances remained at the same level with increasing the Phen-NaDPO concentration in the active layer from 0.25 to 1 wt%.Furthermore, this approach could be proven to effectively work with other cathodes such as bare ITO and ITO/AZO. The self-organization of Phen-NaDPO through spontaneous vertical phase separation is mainly attributed to its high surface energy and strong interaction with the cathode material. The present results highlight that a self-organized cathode interfacial material processed from a "ternary" active layer is fully compatible with the requirements for roll-to-roll fabrication of inverted organic solar cells.

A Self‐Organized Poly(vinylpyrrolidone)‐Based Cathode Interlayer in Inverted Fullerene‐Free Organic Solar Cells

“…The contact angles (θs) of water on PVP, PBDB‐TF, and IT‐4F films were tested to experimentally compare the surface energies of PVP and AL materials. Generally, a higher θ value means a higher surface energy . As shown in Figure c, the neat PBDB‐TF and IT‐4F films are hydrophobic and present much higher θ values than that of the PVP film, meaning that PVP has a higher surface energy than that of PBDB‐TF and IT‐4F.…”

Use of the Phen‐NaDPO:Sn(SCN)2 Blend as Electron Transport Layer Results to Consistent Efficiency Improvements in Organic and Hybrid Perovskite Solar Cells

“…Building on the BCP success, a number of other small molecules, such as bathophenanthroline (Bphen), zwitterions, pyridine derivatives, and a variety of self‐assembled ionic liquids, have been reported and shown to improve electron extraction in OSCs by providing suitable energy‐level matching with the active layer. Among them, 3‐[6‐(diphenylphosphinyl)‐2‐naphthalenyl]‐1,10‐Phenanthroline (Phen‐NaDPO) was shown to combine high electron mobility with good solubility in common solvents that are orthogonal to the organic active layer, enabling the development of OSCs with PCE of over 8.5% …”

Triarylphosphine Oxide as Cathode Interfacial Material for Inverted Perovskite Solar Cells

“…As shown in earlier work, properly selected interfacial layers may reduce the work function by the formation of interfacial dipoles between the metal and the organic interfacial layer. This is likely related to a strong interaction that exists at the interface between PO and Ag, and also between rigid phenanthrolinyl moiety and Ag, which can promote good electrical contact properties between DPO and Ag cathode . The VBM of ZnO (7.6 eV) is sufficient to block holes from the MAPbI 3 layer.…”