Efficiency Enhancement of Inverted Polymer Solar Cells Using Ionic Liquid-functionalized Carbon Nanoparticles-modified ZnO as Electron Selective Layer

Abstract

ZnO thin film was fabricated on tin-doped indium oxide electrode as an electron selective layer of inverted polymer solar cells using magnetron sputtering deposition. Ionic liquid-functionalized carbon nanoparticles (ILCNs) film was further deposited onto ZnO surfaces by drop-casting ILCNs solution to improve interface properties. The power conversion efficiency (PCE) of inverted polymer solar cells (PSCs) with only ZnO layer was quickly decreased from 2.7% to 2.2% when the thickness of ZnO layer was increased from 15 nm to 60 nm. However, the average PCE of inverted PSCs with ZnO layer modified with ILCNs only decreased from 3.5% to 3.4%, which is comparable to that of traditional PSCs with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) anode buffer layer. The results suggested that the contact barrier between ZnO layer and poly(3-hexylthiophene) and phenyl-C61-butyric acid methylester (P3HT:PCBM) blended film compared to ZnO bulk resistance can more significantly influence the performance of inverted PSCs with sputtered ZnO layer. The vanishment of negative capacitive behavior of inverted PSCs with ILCNs modified ZnO layer indicated ILCNs can greatly decrease the contact barrier of ZnO/P3HT:PCBM interface.

Highly Efficient and Air Stable Inverted Polymer Solar Cells Using LiF-Modified ITO Cathode and MoO3/AgAl Alloy Anode

“…A solution-processed ZnO interlayer is commonly used as a good electron transport/collection layer in inverted PSCs, due to its high transparency, high electron mobility and air stability. It becomes important to improve the photocurrent and fill factor of PSCs by appropriate modification of the ZnO interlayer to optimize the contact properties at the ZnO/ITO and ZnO/organic interfaces, and to suppress the carrier traps induced by the defects in the ZnO interlayer. ,, A LiF-modified ITO electrode can lead to a reduction of work function of ITO electrode, which can improve contact quality at the ZnO/ITO interface and help to improve electron extraction in PSCs. , Therefore, a thin LiF-modified ITO electrode was used to achieve the desired contact at the ZnO/ITO interface and to improve further the PCE of AgAl-based cells. Figure c shows the PCE values of AgAl anode-based cells with different thickness of LiF interfaces.…”

“…However, ZnO-based PSCs usually suffer from serious interfacial recombination due to defect induced recombination at the interface between ZnO and the active layer. Recently, fullerene derivative, conjugated polyelectrolytes and ionic liquid functionalized carbon nanoparticles, , have been reported to modify a ZnO layer to optimize contact properties between ZnO and a photoactive layer and/or passivate traps of bulk ZnO layer, improving the photocurrent and fill factor of PSCs. Liao et al reported that PSCs exhibit the improved PCE values from 8.25% to 10.31% using a dual-doped ZnO film, due to improved surface conductivity and enhanced electron mobility.…”