Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 12, Issue 11, Pages 2770-2779Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.1c00335
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Funding
- National Research Foundation of Korea (NRF) - Ministry of Science [NRF-2019R1A2C3009157, 2018K1A3A1A32055268]
- Korea Institute of Energy Technology Evaluation and Planning (KETEP) - Korea government (MOTIE) [20203040010320]
- Korea Evaluation Institute of Industrial Technology (KEIT) [20203040010320] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
- National Research Foundation of Korea [2018K1A3A1A32055268] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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In this study, nickel oxides (NiO) were deposited as hole transport layers (HTLs) in perovskite solar cells (PSCs) with controlled thickness by atomic layer deposition (ALD). Ultrafast transient absorption spectroscopy (TAS) showed ground state bleaching (GSB) recovery, indicating backward hole injection between perovskites and NiO HTLs due to their similar valence band (VB) energy positions. The thickness increase of NiO HTLs induced a red-shift in the photoinduced hole absorption spectrum and a decrease in photoluminescence intensity in near-infrared (NIR) femtosecond TAS.
Nickel oxides (NiO) as hole transport layers (HTLs) in inverted-type perovskite solar cells (PSCs) have been widely studied mainly because of their high stability under illumination. Increases in the power conversion efficiency (PCE) with NiO HTLs have been presented in numerous reports, although the photoluminescence (PL) quenching behavior does not coincide with the PCE increase. The dynamics of the charge carrier transport between the NiO HTLs and the organic-inorganic halide perovskite absorbers is not clearly understood yet and quite unusual, in contrast to organic/polymerics HTLs. We deposited NiO HTLs with precisely controlled thicknesses by atomic layer deposition (ALD) and studied their photovoltaic performances and hole transfer characteristics. Ground state bleaching (GSB) recovery was observed by ultrafast transient absorption spectroscopy (TAS), which suggested that backward hole injection occurred between the perovskites and NiO HTLs, so that the uncommon PL behaviors can be clearly explained. Backward hole injection from the NiO HTL to the perovskite absorber originated from their similar valence band (VB) energy positions. The thickness increase of the NiO HTLs induced VB sharing, which caused a red-shift of the photoinduced hole absorption spectrum in near-infrared (NIR) femtosecond TAS and a decrease in the PL intensity. Our studies on inorganic metal oxide transport layers, NiO in this work, with a thickness dependence and the comparison with organic layers provide a better understanding of the interfacial carrier dynamics in PSCs.
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