Organic and inorganic surface passivations of TiO2 nanotube arrays for dye-sensitized photoelectrodes

Abstract

Surface passivation of photoelectrodes is widely used to improve the performance of dye-sensitized solar cells (DSCs). We use the organic and inorganic materials as a surface-passivating layer of photoelectrodes and introduce the effect of surface passivation on the power conversion efficiency of DSCs. TiO2 nanotube arrays are fabricated by anodic oxidation of Ti foil for photoelectrodes of DSCs. Surface passivating layers are conducted by immersing photoelectrode in various precursor solutions. MgO and WO3 are selected for inorganic passivation. PC61BM is used for organic passivation. In case of inorganic passivation, a basic material (MgO) which has a high isoelectric point (pl >7) shows higher power conversion efficiency of 2.63% by increasing of open circuit voltage (V-oc) to 0.74 V than bare sample of 2.55%. But, an acidic material (WO3) shifts V-oc to low potential resulting in a worse efficiency of DSCs. In case of organic passivation, PC61BM enhances photocurrents and decreases V-oc value compared to bare sample. The power conversion efficiency of PC61BM-coated DSCs is overall improved due to enhanced photocurrents despite of V-oc offset to low potential. Back-transfer electron blocking, dye adsorption, TiO2 conduction band shifting, and additional charge generation by surface passivation are discussed.