Silver nanoparticles-incorporated Nb2O5 surface passivation layer for efficiency enhancement in dye-sensitized solar cells.

Guiding and capturing photons at the nanoscale by means of metal nanoparticles and interfacial engineering for preventing back-electron transfer are well documented techniques for performance enhancement in excitonic solar cells. Drifting from the conventional route, we propose a simple one-step process to integrate both metal nanoparticles and surface passivation layer in the porous photoanode matrix of a dye-sensitized solar cell. Silver nanoparticles and Nb2O5 surface passivation layer are simultaneously deposited on the surface of a highly porous nanocrystalline TiO2 photoanode, facilitating an absorption enhancement in the 465 nm and 570 nm wavelength region and a reduction in back-electron transfer in the fabricated dye-sensitized solar cells together. The TiO2 photoanodes were prepared by spray pyrolysis deposition method from a colloidal solution of TiO2 nanoparticles. An impressive 43% enhancement in device performance was accomplished in photoanodes having an Ag-incorporated Nb2O5 passivation layer as against a cell without Ag nanoparticles. By introducing this idea, we were able to record two benefits - the metal nanoparticles function as the absorption enhancement agent, and the Nb2O5 layer as surface passivation for TiO2 nanoparticles and as an energy barrier layer for preventing back-electron transfer - in a single step.

Ag@Nb2O5 plasmonic blocking layer for higher efficiency dye-sensitized solar cells.

Engineering photons on a nanoscale via guidance and localization by metal nanostructures has a profound influence on the performance of devices that try to mimic the process of photosynthesis. The conventional route for the synthesis of plasmonic nanoparticles and their integration into the porous structure of the photoanode either directly or after being capped with a dielectric material not only adds to the complexity but also to the cost of the cell. The present study introduces the concept of a plasmonic blocking layer that concurrently acts as a light harvester and an electron-blocking layer in a dye-sensitized solar cell (DSSC), wherein the plasmonic silver nanoparticles are incorporated into an Nb2O5 blocking layer by a simple one-step process. The cell with the plasmonic blocking layer achieves an efficiency of 9.24% when compared with a cell with a non-plasmonic blocking layer (7.6%), registering an impressive enhancement in the efficiency by 22%. Moreover, the cell with the plasmonic blocking layer shows an improvement in the efficiency by 49% when compared with the cell without a blocking layer (6.19%).

On the physics of dispersive electron transport characteristics in SnO2 nanoparticle-based dye sensitized solar cells.

The present study elucidates dispersive electron transport mediated by surface states in tin oxide (SnO2) nanoparticle-based dye sensitized solar cells (DSSCs). Transmission electron microscopic studies on SnO2 show a distribution of ∼10 nm particles exhibiting (111) crystal planes with inter-planar spacing of 0.28 nm. The dispersive transport, experienced by photo-generated charge carriers in the bulk of SnO2, is observed to be imposed by trapping and de-trapping processes via SnO2 surface states present close to the band edge. The DSSC exhibits 50% difference in performance observed between the forward (4%) and reverse (6%) scans due to the dispersive transport characteristics of the charge carriers in the bulk of the SnO2. The photo-generated charge carriers are captured and released by the SnO2 surface states that are close to the conduction band-edge resulting in a very significant variation; this is confirmed by the hysteresis observed in the forward and reverse scan current-voltage measurements under AM1.5 illumination. The hysteresis behavior assures that the charge carriers are accumulated in the bulk of electron acceptor due to the trapping, and released by de-trapping mediated by surface states observed during the forward and reverse scan measurements.