Improved electron extraction by a ZnO nanoparticle interlayer for solution-processed polymer solar cells

Abstract

Charge injection/extraction properties dictate the device characteristics of polymer solar cells. Based on a model system comprising PTB7-Th:PC 71 BM blends, we investigate solvent effects and interface properties of ZnO nanoparticles used as electron-transporting/hole blocking interlayers (ETL/HBL) to improve the solar cell performance and stability. We find that the polarity of processing solvents and thickness of ZnO nanoparticles ETL both play a crucial role in the device behavior. Under the optimal conditions, the power conversion efficiency (PCE) is increased from 8.4% to 9.2% for PTB7-Th:PC 71 BM solar cells with a conventional device architecture, which is among the highest efficiencies for this blend system. The simultaneous increase in short-circuit current (J sc ) and fill factor (FF) originates from an effective hole blocking mechanism provided by the ZnO layers which increase the selectivity of charge extraction and reduce non-geminate charge recombination. The dense and air-stable ZnO ETLs minimize the diffusion of moisture and O 2 into the photoactive layer, leading to drastically improved device stability.

Synthesis, growth mechanism, optical properties and catalytic activity of ZnO microcrystals obtained via hydrothermal processing

“…1,2 Studies have demonstrated the versatility and potential capability of ZnO for a wide range of applications in photonic, photovoltaic and electronic devices, such as light-emitting diodes (LEDs), lasers, UV detectors, transistors and solar cells. [3][4][5][6][7][8][9] ZnO also exhibits interesting piezoelectric properties that permit its application as transducers and surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices. 10,11 Furthermore, especially in the form of powder, ZnO can be applied to pigments, 12 photo(catalysts).…”

Interfacial ZnO Modification Using a Carboxylic Acid Functionalized N-Annulated Perylene Diimide for Inverted Type Organic Photovoltaics

“…Interface engineering has played an important role in improving the performance of solution processed bulk-heterojunction (BHJ) organic photovoltaic (OPV) devices. , Among the many different types of interface materials reported, zinc oxide (ZnO) thin-films are the most commonly used cathodic interlayers for inverted type OPVs . ZnO is a good electron transport material, has an appropriate work function for electron extraction, can be easily solution processed, and exhibits reasonable environmental stability. , The modification of ZnO surfaces with organic materials can have a positive impact on charge carrier collection and consequently improve OPV performance …”

Impact of inkjet printed ZnO electron transport layer on the characteristics of polymer solar cells

“…The MO interlayer provides higher stability and lower ohmic contact resistance than the PEDOT:PSS equivalent in conventional PSCs. [11][12][13] As the electron transport layer (ETL) poly [(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-uorene)-alt-2,7-(9,9-dioctyl-uorene)] (PFN), 4,14,15 zinc oxide (ZnO) 16,17 and titanium oxide (TiOx) 9,10,18 are commonly used. ZnO has attracted much interest due to its high transparency, high air-stability and high electron mobility.…”