Atomic Layer Deposition of TiO₂ for a High-Efficiency Hole-Blocking Layer in Hole-Conductor-Free Perovskite Solar Cells Processed in Ambient Air

Abstract

In this study we design and construct high-efficiency, low-cost, highly stable, hole-conductor-free, solid-state perovskite solar cells, with TiO2 as the electron transport layer (ETL) and carbon as the hole collection layer, in ambient air. First, uniform, pinhole-free TiO2 films of various thicknesses were deposited on fluorine-doped tin oxide (FTO) electrodes by atomic layer deposition (ALD) technology. Based on these TiO2 films, a series of hole-conductor-free perovskite solar cells (PSCs) with carbon as the counter electrode were fabricated in ambient air, and the effect of thickness of TiO2 compact film on the device performance was investigated in detail. It was found that the performance of PSCs depends on the thickness of the compact layer due to the difference in surface roughness, transmittance, charge transport resistance, electron-hole recombination rate, and the charge lifetime. The best-performance devices based on optimized TiO2 compact film (by 2000 cycles ALD) can achieve power conversion efficiencies (PCEs) of as high as 7.82%. Furthermore, they can maintain over 96% of their initial PCE after 651 h (about 1 month) storage in ambient air, thus exhibiting excellent long-term stability.

Optimization of a compact layer of TiO2via atomic-layer deposition for high-performance perovskite solar cells

“…Aer the roughness reached the maximum at the lm thickness of 200 nm, the lling of the rugged surface with TiO 2 nanoparticles in another layer is supposed to decrease the surface roughness. Although the rough surface is reported to affect the scattering and transmittance between HBL and PSK, 41 the results of nite-difference time-domain (FDTD) simulation indicate that the difference of R rms from 10 to 40 nm scarcely affects the absorption, as shown in Fig. S3.…”

Perovskite Solar Cells: From the Laboratory to the Assembly Line

“…Hu et al designed hole-conductor-free PSCs in ambient air, startingfrom pinhole-freeT iO 2 films deposited by ALD technology and choosing carbon as the back-electrode. [116] The bestperformance devices required 2000 ALD cycles and achieved PCEs as high as 7.82 %, maintaining 96 %o fi ts original efficiency after 651 ho fs toragei na mbient air.I slavath et al showed that phase-pure crystalline MAPbI 3 perovskite films instantly formed in ambient air at room temperature by at wo-step spin coating process, underminingt he need ford ry atmosphere and post-annealing. [117] PSCs keeping the configurationF TO/ TiO 2 /MAPbI 3 /Spiro-OMeTAD/Au achieved a V oc up to 990 mV and short-circuit current density (J sc )o f2 0.31 mA cm À2 ,b eing quite comparable with values measured for glove-box-processed devices.…”

“…Hu et al. designed hole‐conductor‐free PSCs in ambient air, starting from pinhole‐free TiO 2 films deposited by ALD technology and choosing carbon as the back‐electrode . The best‐performance devices required 2000 ALD cycles and achieved PCEs as high as 7.82 %, maintaining 96 % of its original efficiency after 651 h of storage in ambient air.…”

Highly Compact TiO2 Films by Spray Pyrolysis and Application in Perovskite Solar Cells

“…The ETM often consists of a bilayer constituted by a compact (c‐TiO 2 ) and mesoporous titania (m‐TiO 2 ) junctions engineered to reduce hysteresis and improve charge transfer . For this purpose, TiO 2 films have been deposited using various techniques, like spin‐coating, spray pyrolysis, and atomic layer deposition (ALD) to control their grain size, conformity and compactness.…”