Distinctive Nanocrater Structures in Hybrid Electron‐Collecting Buffer Layers for High Efficiency Polymer:Nonfullerene Solar Cells

Abstract

Here distinctive nanocrater structures generated in the low temperature‐processed hybrid electron‐collecting buffer layers (h‐ECBLs), consisting of zinc oxide (ZnO) and poly(2‐ethyl‐2‐oxazoline) (PEOz), for high efficiency inverted‐type polymer:nonfullerene solar cells are reported. The ZnO:PEOz h‐ECBLs are prepared from their precursor films via thermal annealing at 110–130 °C, which is far lower than conventional condition (200 °C). Results show that the power conversion efficiency (PCE) of solar cells is noticeably improved by introducing the h‐ECBLs with 6 wt% PEOz but turned down at higher PEOz contents irrespective of the annealing temperature (from 9.25% to 11.41% at 120 °C and from 10.19% to 12.03% at 130 °C). The improved PCE is explained by the increased electron mobility in the h‐ECBLs (6 wt%) due to the reduced oxygen deficiency of ZnO by the PEOz components as well as the generated nanocrater (wrinkled at 120 °C) structures leading to the enhanced interfacial area and contact with the active layers.

Pivotal Role of Middle Subcell Thickness on the Performance of Triple‐Junction Tandem Polymer Solar Cells

“…[ 36–38 ] Very recently, our group reported that stable double‐junction tandem PSCs could be fabricated by using the nanocrated interconnection layers based on ZnO:PEOz (zinc oxide:poly(2‐ethyl‐2‐oxazoline)) films. [ 39–41 ] However, only limited studies have been so far reported on the triple‐junction tandem PSCs (best PCE = 11.83%), even though the device performances can be further improved by adding more subcells. [ 42,43 ]…”

“…c) Flat energy band (level) diagram for the present triple‐junction tandem PSC (note that the minus sign and “eV” unit are not shown to avoid crowding the diagram): The HOMO, LUMO, and work function values were taken from our previous reports and literatures. [ 39–41,44–46 ]…”

“…After moving the F‐BHJ layer‐coated samples into a vacuum chamber, the MoO 3 (thickness = 10 nm) and Ni (thickness = 6.5 nm) layers were successively deposited by thermal evaporation. After taking out the samples, the ZnO:PEOz layers were spin‐coated onto the Ni layer‐deposited samples, followed by thermal annealing at 140 °C for 1 h. [ 38–40 ] Next, the M‐BHJ layers (PBDB‐T:IT‐M, thickness = 20–100 nm) were spin‐coated on the ZnO:PEOz layers. These samples were subjected to the deposition of the MoO 3 /Ni/ZnO:PEOz layers with the sampling process as conducted for the front subcells.…”

“…Next, the ZnO precursor solutions were spun on the ITO‐glass substrates to obtain the ZnO layers and subjected to thermal annealing at 200 °C for 1 h (thickness = 40–45 nm). [ 38–40 ] On top of the annealed ZnO layers, the F‐BHJ layer (PIDTT‐BT:PC 71 BM, thickness = 80 nm) was deposited through spin‐coating and dried at 25 °C inside a nitrogen (N 2 )‐filled glove box. After moving the F‐BHJ layer‐coated samples into a vacuum chamber, the MoO 3 (thickness = 10 nm) and Ni (thickness = 6.5 nm) layers were successively deposited by thermal evaporation.…”

Trap-Filling of ZnO Buffer Layer for Improved Efficiencies of Organic Solar Cells

“…Hybrid CBL consisting of ZnO and poly(2ethyl-2-oxazoline) (PEOz) was also constructed and applied to the inverted non-fullerene OSCs. Due to the reduced oxygen deficiency of ZnO by the introduced PEOz, an improved PCE over 12% was achieved (Seo et al, 2018). Additionally, various other organic materials such as polyethylenimine (PEI) (Liu C. et al, 2017), fullerene derivatives (Liao et al, 2014;Hu et al, 2016), and non-fullerene acceptors (Xie and Wuerthner, 2017;Li et al, 2019) have also been utilized to construct highperformance organic-inorganic hybrid materials by passivating the inherent defects of metal oxide layers and remarkable efficiency improvements were all observed.…”