Solution-processed Ga-TiO2 electron transport layer for efficient inverted organic solar cells

Recent review on electron transport layers in perovskite solar cells

“…However, the mesoporous ETL structures are dissimilar. In DSSC, a thick mesoporous ETL is required to facilitate high dye loading with typical thickness of 10 μm 7‐12 . On the contrary, an approximate thickness of 200 nm is sufficient to generate similar photocurrent in the OIHP solar cell 7‐9 .…”

“…Hence, the initial photovoltaic parameters and stability of ETL-free OIHP devices were generally poor and undesirable. [10][11][12]15 Intentional ETL-free perovskite device was first fabricated by Liu et al in 2014 whereby the ZnO-free solar device showed comparable results to the ZnO ETL solar device of 13.5% and 13.7%, respectively. 17 The similar results were attributed to the increased series resistance in the ZnO ETL solar device but decreased surface recombination, vice versa.…”

“…In essence, the ETL has two major roles. First, the presence of an ETL provides a cascading energy level such that electrons from the perovskite absorber are transported smoothly to the cathode with little charge accumulation 7‐12 . Second, the ETL acts as a hole blocking layer, allowing unipolar transference while reducing carrier recombination tendencies 13 .…”

“…First, the presence of an ETL provides a cascading energy level such that electrons from the perovskite absorber are transported smoothly to the cathode with little charge accumulation. [7][8][9][10][11][12] Second, the ETL acts as a hole blocking layer, allowing unipolar transference while reducing carrier recombination tendencies. 13 As a result, widely reported electron transport materials are typically categorized into the following: (i) n-type metal oxide semiconductors such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), tin (IV) oxide (SnO 2 ), tungsten (IV) oxide (WO 3 ), niobium pentoxide (Nb 2 O 5 ) and zinc stannate (Zn 2 SnO 4 ), (ii) n-type metal sulfide/selenide semiconductor such as cadmium selenide (CdSe), zinc sulfide (ZnS), and molybdenum disulfide (MoS 2 ), and (iii) n-type organic semiconductors such as [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), buckminsterfullerene (C60) and other fullerene derivatives.…”

Understanding the role of inorganic carrier transport layer materials and interfaces in emerging perovskite solar cells

“…106 Besides, metal oxides were also used as a substitute of carbon materials to form nanocomposites with TiO 2 , but were found to be relatively inefficient as ETLs due to the inhibited recombination rate offered by impure phase formation. 107 Therefore, Y, 108 Ga, 109 Zr, 110 and Ru 111 doped and Zr/N 112 and Er–Yb, 113 co-doped TiO 2 nanostructures have also been explored as ETLs to achieve longer carrier lifetimes and higher charge density at the ETL/perovskite interface. Moreover, hydrogen 114 and cadmium 115 have been utilized to alter the recombination resistance and charge carrier density of TiO 2 to further increase the collection efficiency.…”