Full SnO2 double-layer dye-sensitized solar cells: Slowly increasing phenomenon of power conversion efficiency

Abstract

Dye-sensitized solar cells (DSCs) have been proven as effective photovoltaic devices for low-cost and large-scale solar energy conversion applications. Fast electron transport, large specific surface area, and slow interfacial electron recombination are indispensable features for an efficient photoelectrode. In this work, we report full SnO2 double-layer DSCs. SnO2 nanoparticles as electron transport layer and large SnO2 particles as scattering layer (SL) are prepared by the hydrothermal method, respectively. Ultrathin Al2O3 barrier layer on the surface of SnO2 film is formed by immersing in Al (NO3)3 solutions and annealed at atmosphere in turn to retard back transfer of electrons to the electrolyte or to the oxidized dye molecules. Four kind cells with SnO2, SnO2/SL, SnO2/Al2O3 and SnO2/SL/Al2O3 film as photoanodes were fabricated, respectively, and their power conversion efficiency (PCE) was continuously tested for 60 days. The open-circuit voltage (Voc), fill factor (FF) and PCE of four kind cells are gradually improved, while short-circuit current (Jsc) is slightly reduced during testing. As a result, the PCE of the SnO2 based DSC increased from 1.36% (0 day) to 3.5% (20 day), and the PCE of the SnO2/SL/Al2O3 based DSC increased from 2.53% (0 day) to 4.57% (20 day). This novel slow increasing phenomenon of PCE observed in SnO2 DSCs is different from that of TiO2 and ZnO. This kind of structure of DSCs and the slowly increasing phenomenon have far-reaching significance for understanding the working mechanism and increasing efficiency.