Interplay of Optical, Morphological, and Electronic Effects of ZnO Optical Spacers in Highly Efficient Polymer Solar Cells

Abstract

Optical spacers based on metal oxide layers have been intensively studied in poly(3‐hexylthiophene) (P3HT) based polymer solar cells for optimizing light distribution inside the device, but to date, the potential of such a metal oxide spacer to improve the electronic performance of the polymer solar cells simultaneously has not yet be investigated. Here, a detailed study of performance improvement in high efficient polymer solar cells by insertion of solution‐processed ZnO optical spacer using ethanolamine surface modification is reported. Insertion of the modified ZnO optical spacer strongly improves the performance of polymer solar cells even in the absence of an increase in light absorption. The electric improvements of the device are related to improved electron extraction, reduced contact barrier, and reduced recombination at the cathode. Importantly, it is shown for the first time that the morphology of optical spacer layer is a crucial parameter to obtain highly efficient solar cells in normal device structures. By optimizing optical spacer effects, contact resistance, and morphology of ZnO optical spacers, poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6diyl] [3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl] thieno[3,4‐b]thiophenediyl]] (PTB7):[6,6]‐phenyl‐C71‐butyric acid (PC70BM) bulk heterojunction solar cells with conversion efficiency of 7.6% are obtained in normal device structures with all‐solution‐processed interlayers.

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

“…Devices processed with DIO show an average efficiency of 7.4% for nonannealed layers similar to results in our former work. [57] However, although the blend morphology is stable up to 140 °C, we observed strong losses in device performance of up to 40% for post-annealing from 80 °C to 120 °C. These losses are in line with reports in literature [38,39] and are mainly related to strong drops in short-circuit density (J sc ) and fill factor (FF), while the open-circuit voltage (V oc ) stays constant.…”

“…The insert in Figure 4a shows the device structure in which poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and ZnO nanoparticle layers are used as hole and electron extraction layer, respectively, leading to high efficiency solar cells. [57] The completed solar cells were exposed to post-annealing at temperatures from 80 °C to 160 °C during 1 h to study their thermal degradation. Figure 4b depict the evolution of the J-V curves of the devices under thermal stress, while Table S2 (Supporting Information) sums up the corresponding photovoltaic parameters.…”

“…[37] Interfaces between the active layer and outer contacts also play a very important role in device operation and stability as shown recently. [37,57,60] The quality of an interface is influenced by potential charge accumulation and formation of leakage current, which depends on the concentration of donor and acceptor at the contacts. [61,62] Here, we observe that leakage current is reduced after PAS-140 accompanied by an increase in V oc .…”

Ozone Sensors Working at Room Temperature Using Zinc Oxide Nanocrystals Annealed at Low Temperature

“…By High-Resolution Transmission Electron Microscope (HR-TEM) JEOL 3010, ZnO NPs, ZnO NPs drop casted from a diluted solution on a mesh-coated carbon film (Figure 1a), presented a homogeneous size (diameter about 5 nm) and shape dispersions [6,7]. By scanning electron microscope (SEM) a JEOL JSM 6320F, analysis of spin-coated ZnO thin films highlights the formation of uniform and densely packed agglomerates (Figure 1b).…”

“…Thus, we prepared five different sensitive layers with resulting layer thicknesses measured by a Veeco Dektak 6M stylus profiler (Veeco, USA) (see Table 1). Previous studies have shown that 0.2% volume of EA, a short-chain surfactant, gives aggregate-free solution [6,7]. ZnO NPs were deposited by spin coating on rigid substrates to compare the sensing performances for three post-annealing temperatures: 80 °C, 150 °C and 300 °C during 30 min, respectively.…”