Organic/Inorganic Polymer Solar Cells Using a Buffer Layer from All-Water-Solution Processing

Abstract

We present an environmentally friendly polymer solar cell based on a hybrid organic/inorganic device structure from an all-water-solution processing and fabricated using a blend of the hydrophilic conjugated polymer PTEBS and water-dispersible TiO2 nanocrystals. Generally, the low viscosity and high surface tension of the water-based solution inhibits the formation of a homogeneous PTEBS/TiO2 composite film on the transparent electrode (FTO). To overcome this, a TiO2 buffer layer was first spin coated onto the FTO surface to modify and improve the PTEBS/TiO2 film formation. The results show that solar cell performance has been significantly improved by the buffer layer. The fill factor for devices fabricated using the buffer layer is improved by a factor of 2 over those without the buffer layer, and the external energy conversion efficiency is increased by a factor of 4 as a result of improved interfacial contact between the absorbing layer and the electrodes, as well as the improved film morphology. The hydrophilic conjugated polymer and the water dispersible buffer TiO2 are both characterized by UV−vis spectroscopy, which reveals that the polymer has a high absorption coefficient (around 105 cm−1). The buffer TiO2 is transparent in the visible-near-infrared region so that the light will pass through and be harvested by the polymer. X-ray diffraction shows that the TiO2 buffer films primarily consist of anatase crystalline structure. This device offers few negative environmental consequences because no organic solvents will be used.