Controllable phase transformation of titanium dioxide for the high performance polymer solar cells

摘要

As an important electron transport layer, titanium dioxide is intensively studied in the polymer solar cells. Titanium dioxide exists as two main polymorphs which are anatase and rutile. However, the impacts of the presence of either or both of these phases on the performance of polymer solar cells remain unclear. In this work, high quality TiO2 films with controllable polymorphs are deposited via sputtering under room temperature. Pure phase of anatase and rutile are obtained. The distinguishing characteristics of the films were analyzed and PSCs with the structure of ITO/TiO2/PTB7-Th:PC71BM/MoOx/Ag were made. We found a better electron extraction efficiency of anatase which may originated from the band alignment of TiO2 in between ITO and active layer and smaller electron effective mass of anatase. Moreover, the anatase possesses a closer refractive index with ITO and high transparency in the short wavelength range which make it efficiently utilize the induced light. The efficiency of the PSCs has achieved 4.01% for rutile device and 8.26% for anatase device.