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

• We describe the photovoltaic enhancement using an ultrathin TiO2 layer.
• The ultrathin TiO2 layer was obtained by atomic layer deposition (ALD) process.
• Processing temperature was optimized to be 200 °C.
• The solar cell performance improved significantly with aid of 200 °C-ALD TiO2.
• This improvement was attributed to the reduction of the surface defects of TiO2 layer.

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 °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 °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.

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