Molecular Doping Inhibits Charge Trapping in Low-Temperature-Processed ZnO toward Flexible Organic Solar Cells

Abstract

There has been a growing interest in the development of efficient flexible organic solar cells (OSCs) due to their unique capacity to provide energy sources for flexible electronics. To this end, it is required to design a compatible interlayer with low processing temperature and high electronic quality. In this work, we present that the electronic quality of the ZnO interlayer fabricated from a low-temperature (130 °C) sol–gel method can be significantly improved by doping an organic small molecule, TPT-S. The doped TPT-S, on the one hand, passivates uncoordinated Zn-related defects by forming N–Zn bonds. On the other hand, photoinduced charge transfer from TPT-S to ZnO is confirmed, which further fills up electron-deficient trap states. This renders ZnO improved electron transport capability and reduced charge recombination. By illuminating devices with square light pulses of varying intensities, we also reveal that an unfavorable charge trapping/detrapping process observed in low-temperature-processed devices is significantly inhibited after TPT-S doping. OSCs based on PBDB-T-2F:IT-4F with ZnO:TPT-S being the cathode interlayer yield efficiencies of 12.62 and 11.33% on rigid and flexible substrates, respectively. These observations convey the practicality of such hybrid ZnO in high-performance flexible devices.

Organic–inorganic hybrid cathode interlayer materials for efficient organic solar cells

“…Other rylene imide and 2-pyran-4-ylidenemalononitrile based molecules and non-fullerene small molecule acceptors have also been used as dopants, such as a naphthalimide-Schiff base (NS), 54 TPT-S 55 and ITIC. 56 Wen et al reported that TPT-S can be effectively doped into ZnO, delivering high photoconductivity.…”

Polymerized Naphthalimide Derivatives as Remarkable Electron‐Transport Layers for Inverted Organic Solar Cells

“…[13][14][15] Subsequently, a series of organic-inorganic hybrid materials have been developed in order to reduce the surface defects of metallic oxides. [16][17][18][19][20][21][22][23] To this date, the ETLs based on metallic oxides still have to face on great challenges to fit the requirements of flexible applications. [24] Organic ETLs, including small molecules [25][26][27][28] and polymers, [29][30][31][32][33] have the advantages of easy modification of structure, low-temperature processing and easy device fabrication, which are beneficial to developing large-area devices in the future.…”

Anion‐Doped Thickness‐Insensitive Electron Transport Layer for Efficient Organic Solar Cells

“…As expected, these properties offer materials with excellent performances even when the thickness of the ETL reach tens of nanometer, much higher than commonly used electron transport layer materials. [15,[26][27][28][29] In addition to designing new material structures, n-doping is proven to be an efficient alternative method to fabricate highly conductive and thicknessinsensitive ETL. [30][31][32][33] Though some progress has been made, the effects of counter anion on the performances of doped ETL as well as device performances is rarely reported, therefore more studies on the effect of counter anion in these electron transport layers should be carried out.…”