Subnanometer Ga₂O₃ Tunnelling Layer by Atomic Layer Deposition to Achieve 1.1 V Open-Circuit Potential in Dye-Sensitized Solar Cells

Abstract

Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce electron recombination in dye-sensitized solar cells (DSC). The subnanometer coating is achieved using atomic layer deposition (ALD) and leading to a new DSC record open-circuit potential of 1.1 V with state-of-the-art organic D-π-A sensitizer and cobalt redox mediator. After ALD of only a few angstroms of Ga(2)O(3), the electron back reaction is reduced by more than an order of magnitude, while charge collection efficiency and fill factor are increased by 30% and 15%, respectively. The photogenerated exciton separation processes of electron injection into the TiO(2) conduction band and the hole injection into the electrolyte are characterized in detail.

Opportunities of Atomic Layer Deposition for Perovskite Solar Cells

“…The deposition of just one Al 2 O 3 ALD cycle (estimated by GPC in 0.1 nm) leads to an improvement of the efficiency compared to the reference cells (+ 13%). In particular, a significant increase in open circuit voltage (V OC ) from 750 to 824 mV (+10%) is observed, as expected when the recombination rate is reduced (7)(8)(9)(18)(19)(20)(21). While the short circuit current (J SC ) remains constant, also the fill factor (FF) exhibits an improvement (+8%).…”

Surface engineered angstrom thick ZnO-sheathed TiO2 nanowires as photoanodes for performance enhanced dye-sensitized solar cells

“…Substantial improvement in DSSC performance could be attained by engineering the dye-TiO 2 interface in order to: (1) reduce the recombination of charge carriers by both the passivation of surface state traps at the interface and the retardation of the back-transfer of photoinjected electrons from the TiO 2 conduction band to the oxidized red-ox species; (2) increase the injection yields and collection efficiencies of photogenerated carriers from dye to TiO 2 ; and (3) increase the light absorption efficiency by enhancing the amount of dye uptake. Several studies show that high band-gap metal-oxide materials such as In 2 O 3 , ZrO 2 , Al 2 O 3 , Nb 2 O 5 , Ga 2 O 3 and SiO 2 could reduce recombination in DSSCs by blocking the back-transfer of electrons and thus preventing the recombination of electrons with either oxidized dye molecules or the oxidized redox couple (the latter one is thought to be particularly dominant in device performance degradation) [17][18][19][20][21][22] or reducing the density of surface trap states on the TiO 2 surface. 18,23 In addition, some studies demonstrate that metal-oxides like Nb 2 O 5 , SrTiO 3 , ZrO 2 and Al 2 O 3 can contribute to device performance enhancement by inducing a surface dipole at the metal-oxide/dye interface, leading to a negative shi in the TiO 2 conduction band 24 and an enhancement in the injection yield of photo-induced electrons.…”

“…Although ALD is less cost effective compared to other deposition techniques, it ensures the uniform and conformal coating of a pinhole-free, angstromthick metal-oxide layer over the entire substrate surface, which is imperative to improve material/device performance, especially in high aspect ratio features. 15,16,19,21 Taking all these factors into consideration, this work aims to improve DSSC device performance through the surface modication of hydrothermally-grown TiO 2 NWs using sub-nanometer ALDcoated ZnO shell-like interfacial layers. The results show that a composite photoanode formed by an optimally thick ZnO shell wrapped around TiO 2 NWs signicantly enhances the PV performance of the DSSC device by reducing surface trap states on TiO 2 NWs and increasing the dye loading amount without hampering electron injection efficiency, which is the main trade-off when using high band gap metal-oxide-coated NWbased photoanodes.…”

Improving the efficiency of dye-sensitized solar cells by photoanode surface modifications

“…Also, using the ALD technique may lead to low manufacturing costs due to the fast processing times and the small amount of material needed to grow the layers [85]. Chandiran et al [86] presented the first use of a gallium oxide tunneling layer deposited by ALD to significantly reduce electron recombination in DSSCs. The surface of the porous TiO2 photoanode for DSSCs was passivated using a subnanometer-thick Ga2O3 tunneling overlayer.…”