Voc enhancement in polymer solar cells with isobenzofulvene-C60 adducts

Publication Type:

Journal Article

Source:

Org. Electron., Elsevier, Volume 31, p.48-55 (2016)

ISBN:

1566-1199

URL:

http://www.sciencedirect.com/science/article/pii/S1566119916300088

Keywords:

2016

Abstract:

<p>We report the use of isobenzofulvene&ndash;C60 adducts in bulk heterojunction organic solar cells, synthesized via the [4 + 2] cycloaddition of C60 with an in situ generated isobenzofulvene intermediate. The LUMO energy levels of these adducts are 20&ndash;180 meV higher than that of PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). This large increase of the LUMO level is attributed to cofacial &pi;-orbital interactions between the fullerene surface and the isobenzofulvene &pi;&ndash;system (aromatic ring and double bond). Raised LUMO levels of fullerenes, together with their desirably slow recombination dynamics, led to higher open-circuit voltages (VOC) in bulk heterojunction polymer solar cells (up to 0.75 V for bisadducts) relative to cells tested in parallel using the well-known PCBM as the fullerene acceptor. In addition to enhanced VOC, the short-circuit current densities (JSC) were improved in the devices containing the epoxide analogs of the isobenzofulvene&ndash;C60. Notably the epoxide derivative of the monoadduct (IBF&ndash;Ep) exhibited &sim;20% enhancement of power conversion efficiency (PCE) compared to reference P3HT:PCBM solar cells. A combination of optical and electronic methods was used to investigate the origin of the PCE enhancement observed with these new fullerene acceptors with particular attention to the increased VOCs.</p>