Suppressing the Photocatalytic Activity of Zinc Oxide Electron-Transport Layer in Nonfullerene Organic Solar Cells with a Pyrene-Bodipy Interlayer

Abstract

Organic solar cells based on nonfullerene acceptors have recently witnessed a significant rise in their power conversion efficiency values. However, they still suffer from severe instability issues, especially in an inverted device architecture based on the zinc oxide bottom electron transport layers. In this work, we insert a pyrene-bodipy donor–acceptor dye as a thin interlayer at the photoactive layer/zinc oxide interface to suppress the degradation reaction of the nonfullerene acceptor caused by the photocatalytic activity of zinc oxide. In particular, the pyrene-bodipy-based interlayer inhibits the direct contact between the nonfullerene acceptor and zinc oxide hence preventing the decomposition of the former by zinc oxide under illumination with UV light. As a result, the device photostability was significantly improved. The π–π interaction between the nonfullerene acceptor and the bodipy part of the interlayer facilitates charge transfer from the nonfullerene acceptor toward pyrene, which is followed by intramolecular charge transfer to bodipy part and then to zinc oxide. The bodipy-pyrene modified zinc oxide also increased the degree of crystallization of the photoactive blend and the face-on stacking of the polymer donor molecules within the blend hence contributing to both enhanced charge transport and increased absorption of the incident light. Furthermore, it decreased the surface work function as well as surface energy of the zinc oxide film all impacting in improved power conversion efficiency values of the fabricated cells with champion devices reaching values up to 9.86 and 11.80% for the fullerene and nonfullerene-based devices, respectively.

A Novel Conjugated Pyrene-BODIPY Dyad: Synthesis, Characterization and Properties

“…The molecule exhibits a large dipole moment of 4.90 D that enables higher intramolecular charge-transfer rates (41). The dipole moment is higher than that previously reported a similar molecule in the literature (42). The calculations indicate that both HOMO and LUMO levels are placed on the BODIPY unit ( Figure 7).…”

Progress in Materials, Solution Processes, and Long‐Term Stability for Large‐Area Organic Photovoltaics

“…[ 133 ] Photoexcitation by UV light at ZnO produces hydroxyl radicals from adsorbed H 2 O that degrades the nonfullerene acceptor. [ 134 ] To suppress the degradation reaction of the nonfullerene acceptor caused by the photocatalytic activity of ZnO, insertion of a thin interlayer at the interface or surface modification of the ZnO ETL in inverted OPV devices has been extensively studied using lithium doping, [ 135 ] aluminum doping, [ 136 ] magnesium doping, [ 137 ] C 60 self‐assembled monolayers, [ 119 ] pyrene‐bodipy dye, [ 138 ] and the water‐soluble conjugated polyelectrolyte PF EO SO 3 Li. [ 139 ] Surface modification of the ZnO ETL reduces interface trap‐assisted recombination losses and has enhanced their long‐term stability, resulting in extrapolated T80 lifetimes longer than 20 years.…”

Interface Modification Enabled by Atomic Layer Deposited Ultra‐Thin Titanium Oxide for High‐Efficiency and Semitransparent Organic Solar Cells

“…ZnO usually shows strong photocatalytic activity under UV illumination and can cause photodegradation of non-fullerene acceptors. [64,65] Therefore, we conducted the absorption measurement of both fresh and degraded N3 film on ZnO and ZnO/TiO x (two cycles) layers to investigate the degradation effect. The results are shown in Figure S10, Supporting Information.…”