Towards large-area perovskite solar cells: the influence of compact and mesoporous TiO₂ electron transport layers

Abstract

Titanium dioxide (TiO 2 ) is a widely used electron transport material in organic-inorganic hybrid perovskite solar cells (PSCs). In order to reveal the influence of an additional mesoporous TiO 2 (mp-TiO 2 ) layer on fabricating large-area perovskite solar cells using TiO 2 as the electron transport layer, we have conducted a comprehensive study on the solution-processed PSCs with or without an additional mp-TiO 2 layer. Photoemission spectroscopy measurement indicates that, compared with the compact TiO 2 (cp-TiO 2 ) layers, the mp-TiO 2 layers possess a slightly larger work function, which will improve the electron extraction efficiency at the perovskite-TiO 2 interface. The PSCs with an additional mp-TiO 2 layer exhibit better performances than those with only a cp-TiO 2 layer. They suffer from a smaller efficiency loss when enlarging the device area from 0.16 to 1.44 cm 2 and exhibit a better long-term stability. About 89% of the initial efficiency is retained after keeping in dry air for 1000 h for the device with an active area of 1.44 cm 2 . For both cases, increasing the active device area is beneficial to long term stability, photoluminescence measurement indicates that this is result from the degradation of perovskite films starts at the margin of the cells. Our work implies the indispensable role of the additional mp-TiO 2 layer for optimizing the performances of large-area PSCs using TiO 2 as the electron transport layer.

Flexible and Self‐Powered Photodetector Arrays Based on All‐Inorganic CsPbBr3 Quantum Dots

“…[ 47 ] By performing ultraviolet photoelectron spectroscopy (UPS), E f,2 of the CsBr/KBr assisted perovskite layers were determined to be ≈5.54, 5.71, 5.18, 5.13, and 5.06 eV, with increasing the fraction from 0 to 0.3, respectively (Figure S19, Supporting Information). By taking account of the reported value of E f,1 , [ 49 ] the theoretical V bi were calculated as 1.23, 1.40, 0.88, 0.82, and 0.75 eV, respectively. The modulated E f by using the additive‐assisted strategy results in the largest V bi from 0.025 CsBr/KBr treated devices, suggesting more efficient charge separation, transportation, and collection.…”

Electrospun Networks of ZnO‐SnO2 Composite Nanowires as Electron Transport Materials for Perovskite Solar Cells

“…The most frequently used ETLs in the fabrication of PSCs are TiO 2 , ZnO, and SnO 2 [20][21][22][23]. TiO 2 is the most commonly used ETL in PSCs due to its ease of fabrication, favorable energy level alignment, and its long electron lifetime [24]. However, despite being a good absorber of ultraviolet light, the low electron mobility (6:21 × 10 −5 cm 2 /V s) [25], which is responsible for the accumulation of charge at the interface between ETL and perovskite, limits its use in practical PSCs [26,27].…”

Improving stability of organometallic-halide perovskite solar cells using exfoliation two-dimensional molybdenum chalcogenides

“…Normally, adding hole and electron transporting layers (HTL and ETL, respectively) in PSCs between the perovskite layer and the electrodes helps to separate and selectively collect the generated charge carriers (holes at the cathode and electrons at the anode electrode) 21 . To date, TiO 2 is the most widely used ETL material for PSCs to prevent electron-hole recombination at the anode 4,6,22 . This kind of ETL typically consists of compact TiO 2 layer (c-TiO 2 , 50-80 nm) and mesoporous TiO 2 layer (mp-TiO 2 , 200-300 nm) 4,6,22 .…”

“…To date, TiO 2 is the most widely used ETL material for PSCs to prevent electron-hole recombination at the anode 4,6,22 . This kind of ETL typically consists of compact TiO 2 layer (c-TiO 2 , 50-80 nm) and mesoporous TiO 2 layer (mp-TiO 2 , 200-300 nm) 4,6,22 . On the other hand, 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-MeOTAD) represents the reference hole transport material (HTM) used for PSCs due to its facile deposition and high performance 23 .…”

“…(a sketch of the solar cell and its band energy diagram is shown in Fig. 1a and b) 22,29,31,39 . We investigated various preparation conditions of 2D MC HTL buffer layers followed with a characterization of the devices' power conversion efficiency (PCE) and stability.…”