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Choi, Eun Young,Kim, Jincheol,Lim, Sean,Han, Ekyu,Ho-Baillie, Anita W.Y.,Park, Nochang Elsevier 2018 Solar energy materials and solar cells Vol.188 No.-
<P><B>Abstract</B></P> <P>In this work, we employ atomic layer deposition (ALD) to form Al<SUB>2</SUB>O<SUB>3</SUB> layer as an encapsulant for perovskite solar cells (PSCs). Al<SUB>2</SUB>O<SUB>3</SUB> layer deposited at temperature as low as 95 °C achieves water vapor transmission rate (WVTR) of 1.84 × 10<SUP>−2</SUP> g m<SUP>−2</SUP> d<SUP>−1</SUP> at 45 °C–100%RH when thermal ALD is used. In order to test the moisture barrier capability of Al<SUB>2</SUB>O<SUB>3</SUB> layer for PSCs, mesoporous perovskite devices, with spiro-OMeTAD or PTAA as hole transport layer (HTM) encapsulated by 50 nm Al<SUB>2</SUB>O<SUB>3</SUB> film, are exposed to 65 °C–85%RH for 350 h and their stabilities are monitored. We find that the color of perovskite does not change after 350 h of exposure regardless of the type of HTM used. With regards to Th-ALD encapsulated devices, PTAA based PSCs experienced a smaller power conversion efficiency (PCE) drop than spiro-OMeTAD based PSCs after thermal stress at 65 °C. This is due to the presence of pinholes within spiro-OMeTAD layer after thermal stress which are not observed in PTAA. Finally, we successfully achieve excellent durability test results for mesoporous (HC(NH<SUB>2</SUB>)<SUB>2</SUB>PbI<SUB>3</SUB>)<SUB>0.85</SUB>(CH<SUB>3</SUB>NH<SUB>3</SUB>PbBr<SUB>3</SUB>)<SUB>0.15</SUB>/PTAA devices encapsulated by 50 nm Al<SUB>2</SUB>O<SUB>3</SUB> with less than 4% drop in PCE after 7500 h (> 10 months) of exposure to 50%RH under room temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The WVTR values of 50 nm Al<SUB>2</SUB>O<SUB>3</SUB> layers is 1.84 x 10<SUP>−2</SUP> g m<SUP>−2</SUP> d<SUP>−1</SUP> at 45 °C–85 %RH. </LI> <LI> PTAA is more stable than spiro-OMeTAD during ALD process. </LI> <LI> Pinholes are formed within spiro-OMeTAD layer under thermal stress. </LI> <LI> PTAA-based devices experiences less than 4% drop after 7500 h of 50 %RH at room temperature. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Synopsis: This research focused on the method to enhance the stability of perovskite solar cells via Al<SUB>2</SUB>O<SUB>3</SUB> thin film encapsulation. Additionally, degradation mechanism is investigated during ALD process.</P> <P>[DISPLAY OMISSION]</P>
Spatial Distribution of Lead Iodide and Local Passivation on Organo-Lead Halide Perovskite
Chen, Sheng,Wen, Xiaoming,Yun, Jae S.,Huang, Shujuan,Green, Martin,Jeon, Nam Joong,Yang, Woon Seok,Noh, Jun Hong,Seo, Jangwon,Seok, Sang Il,Ho-Baillie, Anita American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.7
<P>We identify nanoscale spatial distribution of PbI2 on the (FAPbI(3))(0.85)(MAPbBr(3))(0.15) perovskite thin film and investigate the local passivation effect using confocal based optical microscopy of steady state and time-resolved photoluminescence (PL). Different from a typical scanning electron microscope (SEM) morphology study, confocal based PL spectroscopy and microscopy allow researchers to map the morphologies of both perovskite and PbI2 grains simultaneously, by selectively detecting their characteristic fluorescent bands using band-pass filters. In this work, we compare the perovskite samples without and with excess PbI2 incorporation and unambiguously reveal PbI2 distribution for the PbI2-rich sample. In addition, using the nanoscale time-resolved PL technique we show that the PbI2-rich regions exhibit longer lifetime due to suppressed defect trapping, compared to the PbI2-poor regions. The measurement on the PbI2-rich sample indicates that the passivation effect of PbI2 in perovskite film is effective, especially in localized regions. Hence, this finding is important for further improvement of the solar cells by considering the strategy of excess PbI2 incorporation.</P>