High performance inverted polymer solar cells using ultrathin atomic layer deposited TiO2 films

Photovoltaic properties of inverted type polymer solar cells (PSCs) using ultrathin TiO2 layers as an adjuvant electron collecting layer were investigated. To prepare the ultrathin (2.5 nm) TiO2 layers on top of TiO2 nanoparticles, atomic layer deposition (ALD) process was conducted at 125, 175, and 200 degrees C. The addition of ALD TiO2 on nanoparticulated TiO2 effectively enhanced the photovoltaic performances of inverted organic solar cells. The inverted PSC device with the thin 200 degrees C-ALD TiO2 layers showed the highest power conversion efficiency of 3.50%, which is an enhancement of approximately 30% compared to the cells without the ALD TiO2 layer (PCE = 2.72%). This work demonstrates that the ALD process plays a critical role in the enhancement of electron extraction efficiency with treating the surface defects of the TiO2 nanoparticles. (C) 2015 Elsevier B.V. All rights reserved.