Band Edge Modulated Polymer Layer to Decrease Back Electron Transfer and Increase Efficiency in Sensitized Solar Cells

Abstract

time scale of electron transport from TiO 2 to conducting glass is in milliseconds. [ 7 ] Thus, the increased residence time of the electron in TiO 2 increases the possibility of BeT with the holes in either dyes or electrolyte. In fact, the recombination of electron in TiO 2 with that of the holes in electrolytes has been found to be one of the major causes of decreased DSSC efficiency. Thus, suppression of BeT process is an effective way to improve the DSSC effi ciency. However, the approach should not affect the electron injection from the dyes to the TiO 2 . One of the approaches to suppress the BeT process is the addition of additives in the redox electrolytes. [ 8,9 ] These additives adsorb on the TiO 2 and decrease the BeT. [ 10 ] Modifi cation of TiO 2 by alkyl silane is another approach to suppress the BeT. [11][12][13] Although these approaches increased the effi ciency of DSSC, the improvement is not very high because the layer thickness is not high. The attempt to use longer alkyl chain silanes with an objective of increasing the thickness did not signifi cantly alter the DSSC effi ciency due to the imperfect coverage of the TiO 2 surface. [ 14,15 ] Several inorganic oxide barrier layers such as Al 2 O 3 , HfO 2 , and In 2 O 3 have been explored as barrier layer. [16][17][18][19] These barrier layers were deposited before dye absorption either by chemical bath deposition or by atomic layer deposition. The insulating nature of these layers affects the charge injection process. Furthermore, the energy levels of the barrier layer also affect the electron transfer dynamics. [ 20 ] Organic polymers have been coated on top of TiO 2 in solid state dye sensitized solar cells with a different objective. An ion-ligating polymer with different ionization potential has been used to facilitate cascade electron transport. [ 21 ] Photo electropolymerized PEDOT was used as hole transport layer in a solid state dye sensitized solar cell without any other electrolyte. The effi ciencies of these cells were 5.6%. [ 22 ] Considering this, a barrier layer that does not affect electron transfer from LUMO of the dye to TiO 2 and electrolyte to the HOMO of the dye is desirable. It will be an added advantage, if the layer is prepared by solution process. Toward this objective, we have used semiconducting polymers with commensurate band edges to retard the BeT process ( Figure 1 a). The polymers with the structures shown in Figure 1 b were tested and found out that a polymer with a HOMO and LUMO levels at −5.8 and −3.1 eV, respectively, can improve the DSSC effi ciency by 22%. The effi ciency Recombination of charges residing in the TiO 2 and redox electrolyte is one of the factors affecting the effi ciency of dye sensitized solar cells (DSSCs). To circumvent this recombination, inorganic oxide barrier layers and organic silanes have been coated on TiO 2 /dyes. Due to the insulating nature of these layers, the effi ciency increase is not very impressive. Conducting polymers with different band edges are used to suppress the cha...

Silk Cocoon as Counter ‐ Electrode Substrate in Dye ‐ Sensitized Solar Cells

“…While using iodolyte (I − /I 3 − ), the semicircle at high frequency region is attributed to reduction of I 3 − . The other semicircle corresponds to the charge transfer impedance at the interface ,. Charge transfer resistance (R ct ) is inversely correlated to the tri‐iodide catalytic activity .…”

“…The other semicircle corresponds to the charge transfer impedance at the interface. [27,28] Charge transfer resistance (R ct ) is inversely correlated to the tri-iodide catalytic activity. [29] The R ct was found to be 3.1 W/cm 2 in case of PEDOTÀG-SCs, which is slightly lower for Pt-FTO (2.4 W/cm 2 ).…”

Nanoporous Reduced Graphene Oxide and Polymer Composites as Efficient Counter Electrodes in Dye-Sensitized Solar Cells

“…In a symmetrical cell (CE/electrolyte/CE), the charge transfer resistance (R ct ) is inversely correlated to the tri-iodide catalytic activity. 36,41 The charge-transfer resistance of the PEDOT:PSS−PG film (0.95 Ω cm −2 ) is found to be close to that of Pt (0.85 Ω cm −2 ). This phenomenon indicates that the PEDOT:PSS−PG film has a reasonably lower interfacial chargetransfer resistance because of their high electrical conductivity and superior electrocatalytic activity.…”

Solution-processed two-dimensional materials for next-generation photovoltaics

“…770 In detail, graphene dispersed in o-dichlorobenzene was uniformly incorporated in a semiconducting polymer with commensurate band edges (P1) (see chemical structure in ref. 771) and the resulting composite (P1-graphene) solution was spin coated over the cell photoanode to act as a barrier layer limiting the back-transfer process of electrons (Fig. 13).…”