Hot-compression: An effective postdeposition treatment for electrophoretically deposited dye-sensitized solar cell

Abstract

In this investigation, low-cost commercial Degussa P25 TiO 2 -based dye-sensitized solar cells (DSCs) have been fabricated using electrophoretic deposition (EPD) along with a new post-deposition treatment named hot-compression. We have optimized the number of deposition layers and found that a four layer electrophoretic deposition gives a homogeneous crack-free photoelectrode. Multilayer deposition minimizes the cracks; while to ensure the uniformity of the deposited film's surface, we introduce a four-layer four-side electrophoretic deposition (4L4SEPD) technique. Then the electrophorically deposited substrates have been post-treated by a hot-compression followed by sintering. Performance of the DSCs fabricated by this way have been compared with the conventional post-treated (sintered, compressed at room temperature) DSCs. About 16%, 39%, and 70% enhancement in power conversion efficiency has been achieved in DSC devices with compression, hot-compression, and hot-compression followed by sintering, respectively as compared to the sintered device. Several characterizations including scanning electron microscopy (SEM), photocurrent-voltage (I-V) measurement, incident photon-to-electron conversion efficiency, transmittance, and electrochemical impedance spectra (EIS) have been employed to find the nature of improvement with the post-treatments. In detail investigations reveal that hot-compression improves the surface morphology, transmittance, and electron transport which in turn lead to a substantial enhancement of photocurrent and power conversion efficiency. Under an optimized hot-compression (40 MPa compression at 70 °C heating) followed by sintering conditions, the overall power conversion efficiency of a device with P25 TiO 2 photoanode has reached to 4.98% under illumination of AM 1.5 G (100 mW · cm−2). This work demonstrates that 4L4SEPD combined with hot-compression post-treatment provides a way to fabricate highly efficiency DSCs.