The importance of dye chemistry and TiCl4 surface treatment in the behavior of Al2O3 recombination barrier layers deposited by atomic layer deposition in solid-state dye-sensitized solar cells

Abstract

Atomic layer deposition (ALD) was used to fabricate Al(2)O(3) recombination barriers in solid-state dye-sensitized solar cells (ss-DSSCs) employing an organic hole transport material (HTM) for the first time. Al(2)O(3) recombination barriers of varying thickness were incorporated into efficient ss-DSSCs utilizing the Z907 dye adsorbed onto a 2 μm-thick nanoporous TiO(2) active layer and the HTM spiro-OMeTAD. The impact of Al(2)O(3) barriers was also studied in devices employing different dyes, with increased active layer thicknesses, and with substrates that did not undergo the TiCl(4) surface treatment. In all instances, electron lifetimes (as determined by transient photovoltage measurements) increased and dark current was suppressed after Al(2)O(3) deposition. However, only when the TiCl(4) treatment was eliminated did device efficiency increase; in all other instances efficiency decreased due to a drop in short-circuit current. These results are attributed in the former case to the similar effects of Al(2)O(3) ALD and the TiCl(4) surface treatment whereas the insulating properties of Al(2)O(3) hinder charge injection and lead to current loss in TiCl(4)-treated devices. The impact of Al(2)O(3) barrier layers was unaffected by doubling the active layer thickness or using an alternative ruthenium dye, but a metal-free donor-π-acceptor dye exhibited a much smaller decrease in current due to its higher excited state energy. We develop a model employing prior research on Al(2)O(3) growth and dye kinetics that successfully predicts the reduction in device current as a function of ALD cycles and is extendable to different dye-barrier systems.

Towards Long‐Term Photostability of Solid‐State Dye Sensitized Solar Cells

“…No clear difference in recombination dynamics between 1AS, 5AS, and 20AS films was observed, indicating that most of the inhibition of recombination arises from the first shell layer . Despite the inhibition of recombination with the alumina‐silicate shells, solar cells fabricated from such films still exhibited a similar deterioration in performance when exposed to simulated sun light in an inert atmosphere, as we shown in Figure 4 .…”

“…This is also consistent with the increased photocurrents measured in the solar cells compared to the control device, and suggests that the chemical bath method for growing alumina‐silicate may not necessarily grow a thick shell, but rather a surface passivation layer. Shells thicker than 1 nm are expected to reduce injection yield and hence photocurrent …”

Impact of Conformality and Crystallinity for Ultrathin 4 nm Compact TiO2 Layers in Perovskite Solar Cells

“…The spray‐pyrolysis precursor solution was titanium diisopropoxide bis(acetylacetonate) in ethanol. The exact deposition parameters used are taken from those in literature and our previous work on DSSCs and QDSSCs, and are detailed in the experimental section. A manual spray‐pyrolysis process was used, which aerosolizes the precursor solution.…”

Nanoengineering Energy Conversion and Storage Devices via Atomic Layer Deposition

“…So far, the most investigated ALD materials for the photoanodes include TiO 2 , ZnO, and Al 2 O 3 . The TiO 2 and ZnO were usually used as the active films, while the ultrathin TiO 2 and Al 2 O 3 were more studied as the interfacial films. There still have some other materials been explored as the potential passivation layers, such as HfO 2 , ZrO 2 , Ga 2 O 3 , Nb 2 O 5 , Ta 2 O 5 , and In 2 S 3 …”