Organic/inorganic polymer solar cells using a buffer layer from all-water-solution processing

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.