Effects of TiO₂ Interfacial Atomic Layers on Device Performances and Exciton Dynamics in ZnO Nanorod Polymer Solar Cells

Abstract

The performances of organic electronic and/or photonic devices rely heavily on the nature of the inorganic/organic interface. Control over such hybrid interface properties has been an important issue for optimizing the performances of polymer solar cells bearing metal-oxide conducting channels. In this work, we studied the effects of an interfacial atomic layer in an inverted polymer solar cell based on a ZnO nanorod array on the device performance as well as the dynamics of the photoexcited carriers. We adopted highly conformal TiO2 interfacial layer using plasma enhanced atomic layer deposition (PEALD) to improve the compatibility between the solution-prepared active layer and the ZnO nanorod array. The TiO2 interfacial layer facilitated exciton separation and subsequent charge transfer into the nanorod channel, and it suppressed recombination of photogenerated carriers at the interface. The presence of even 1 PEALD cycle of TiO2 coating substantially improved the short-circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF), leading to more than 2-fold enhancement in the power conversion efficiency (PCE). The dynamics of the photoexcited carriers in our devices were studied using transient absorption (TA) spectroscopy. The TA results clearly revealed that the TiO2 coating played a key role as an efficient quencher of photogenerated excitons, thereby reducing the exciton lifetime. The electrochemical impedance spectra (EIS) provided further evidence that the TiO2 atomic interfacial layer promoted the charge transfer at the interface by suppressing recombination loss.

Control of charge dynamics by blending ZnO nanoparticles with poly(3-hexylthiophene) for efficient hybrid ZnO nanorods/polymer solar cells

“…Various development approaches for efficient materials and well-designed device structures have been investigated to achieve enhanced power conversion efficiency (PCE) of HPV devices [5,6]. Among the developed nanomaterials, ZnO nanorod arrays, which can be grown vertically from a substrate, have great potential for HPV applications because of their ease of synthesis [7,8] and high electron mobilities (*10 2 cm 2 V -1 s -1 ) [9] with a direct transport pathway to the electrode [10,11].…”

“…To overcome the problematic limitation, the concept of bulk heterojunction (BHJ), which has been extensively utilized in organic photovoltaic (OPV) devices [23][24][25], can be performed in the hybrid ZnO/P3HT system. In the concepts of BHJ, donor/acceptor blend films with selfassembled phase separation are able to provide shorter distance for mobile excitons to the interfaces.…”

Fabrication of Organic Solar Cells based on Photosensitive Small Molecules and Study of Electron Acceptor Layer Effect on Efficiency

“…ZnO is a wide band gap semiconductor with an energy gap of 3.3 eV and a conduction band edge of 4.3 eV. This band edge is sufficiently high to extract electrons from typical donor and acceptor molecules and/or polymers [10]. There are many methods used for the ZnO deposition like spin coating, atomic layer deposition, screen printing, nano-imprinting, pulsed laser deposition, spin-cast and spray coating etc [10][11][12][13][14].…”

“…This band edge is sufficiently high to extract electrons from typical donor and acceptor molecules and/or polymers [10]. There are many methods used for the ZnO deposition like spin coating, atomic layer deposition, screen printing, nano-imprinting, pulsed laser deposition, spin-cast and spray coating etc [10][11][12][13][14]. Diego Barrera et al reported thermal annealing of P 3 HT:PCBM bulk heterojunctions (BHJs) on top of a commonly used sol-gel ZnO electron transport layer leading to the formation of PCBM clusters [15].…”

Impedance spectroscopy analysis on the effects of TiO2 interfacial atomic layers in ZnO nanorod polymer solar cells: Effects of interfacial charge extraction on diffusion and recombination

“…Several groups have exploited thin layers of self-assembled organic dyes or small molecules [25][26][27][28][29][30][31][32][33] to improve the affinity between the oxide surface and the organic active layer. Employing ZnO-TiO 2 core-shell nanorods has been another alternative to improve ZnO interfacial properties since TiO 2 provides higher chemical stability and passivation of surface defects [34][35][36][37][38][39][40]. Several studies have shown improved photovoltaic performances by applying various methods of TiO 2 coatings on ZnO nanorods [34][35][36][37][38][39][40].…”