Abstract
With state-of-the-art organic solar cells (OSCs) surpassing 16% efficiency, stability becomes critical for commercialization. In this work, the power of using photoluminescence (PL) measurements on plain films is demonstrated, as well as high-performance liquid chromatography analysis to reveal the origin of UV instabilities in OSCs based on the most commonly used acceptors PC70BM ([6,6]-phenyl-C71-butyric acid methyl ester), ITIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene), and o-IDTBR (indacenodithiophene-based non-fullerene acceptor). The UV dependent stability tests reveal instabilities in solar cells based on PC70BM and ITIC while devices based on o-IDTBR are highly stable even under UV illumination. The analysis of solar cell devices based on charge extraction and sub-bandgap external quantum efficiency only shows the UV-dependent emergence of traps, while PL spectra of plain films on glass allows the disentanglement and identification of individual instabilities in multi-component bulk-heterojunction devices. In particular, the PL analysis demonstrates UV instabilities of PC70BM and ITIC toward the processing additive 1,8 diiodooctane (DIO). The chemical analysis reveals the in-depth mechanism, by providing direct proof of photochemical reactions of PC70BM and ITIC with UV-induced radicals of DIO. Based on this scientific understanding, it is shown how to stabilize PBQ-QF:PC70BM devices.