There are several recommendations for future work. First, this current work was limited to passivation of PMMA at the top side of MAPbI3 film. At the glass|MAPbI3 interface, there is no passivation mechanisms. Hence, there may be degradation occurring at the glass|MAPbI3 interface. Attempt to spin- coat MAPbI3 on top of hydrophobic PMMA layer had been made, but the precursor solution has poor wettability on the PMMA layer and was flung off without being deposited on the PMMA layer during spin-coating. In theory, the surface of PMMA can be made more hydrophilic by activating the surface using UV-ozone cleaner, whereby the ozone attacks the surface of PMMA layer, making them more hydrophilic. Therefore, it is recommended to investigate dual passivation effect on thermal stability of MAPbI3 in the future.
Second, since the passivation was only on the top side of MAPbI3 film.
As such, there is also probability that degradation occurred at the unsealed edge sides of the film. In conjunction with the first recommendation, future work should remedy this to achieve higher thermal stability of the film.
Third, the methods used in this work to enhance thermal stability of MAPbI3 film at 150 °C may be used on other more thermally stable FA-Cs perovskite material. One should expect better thermal endurance from these newer perovskite materials.
Fourth, the VOx sol preparation in this work represents the worst-case scenario, whereby the concentration of the VO(acac)2 in IPA was saturated. In
saturated solution, the amount of acetylacetonate in IPA was maximum, hence possessing maximum risk of degradation by solvents. Previous works by Guo et al. (2018) and Tan et al. (2012) only employed maximum concentration of 10 mg/mL in ethanol, and 1.5 mg/mL in IPA. Therefore, one should expect less or negligible damage to the PMMA encapsulated film in the future by employing low concentration VOx sol.
Finally, as the incorporation of VOx proven to be promising, fabrication of PSC with configuration of FTO|SnO2|MAPbI3|VOx|Cu CE is enticing. Future work should investigate the performance (e.g., open circuit voltage (Voc), short- circuit current density (Jsc), fill-factors (FF), and PCE) and thermal stability of the device. Successful fabrication of such device should contribute to accelerated commercialization of PSC.
126
LIST OF REFERENCES
Alsulami, A. et al., 2016. Thermally stable solution processed vanadium oxide as a hole extraction layer in organic solar cells. Materials (Basel). 9, 235.
Bao, Q., Liu, X., Braun, S., Fahlman, M., 2014. Oxygen- and water-based degradation in [6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PCBM) films. Adv. Energy Mater. 4, 1301272.
Bi, D. et al., 2016. Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%. Nat.
Energy 1, 16142.
Bi, E. et al., 2017. Diffusion engineering of ions and charge carriers for stable efficient perovskite solar cells. Nat. Commun. 8, 15330.
Boyd, C.C. et al., 2018. Barrier design to prevent metal-induced degradation and improve thermal stability in perovskite solar cells. ACS Energy Lett.
3, 1772–1778.
Bu, T. et al., 2018. Universal passivation strategy to slot-die printed SnO2 for hysteresis-free efficient flexible perovskite solar module. Nat. Commun.
9, 4609.
Cacovich, S. et al., 2017. Gold and iodine diffusion in large area perovskite solar cells under illumination. Nanoscale 9, 4700–4706.
Chan, S.-H., Chang, Y.-H., Wu, M.-C., 2019. High-performance perovskite solar cells based on low-temperature processed electron extraction layer.
Front. Mater. 6, 1–7.
Chaudhary, B. et al., 2020. Mixed-dimensional naphthylmethylammonium- methylammonium lead iodide perovskites with improved thermal stability. Sci. Rep. 10, 429.
Chen, Changsong et al., 2020. Flexible inorganic CsPbI3 perovskite nanocrystal-PMMA composite films with enhanced stability in air and water for white light-emitting diodes. Nanotechnology 31, 225602.
Chen, Q. et al., 2014. Controllable self-induced passivation of hybrid lead iodide perovskites toward high performance solar cells. Nano Lett. 14, 4158–4163.
127
Chen, Y., Zhou, H., 2020. Defects chemistry in high-efficiency and stable perovskite solar cells. J. Appl. Phys. 128.
Cheng, Y. et al., 2017. 18% high-efficiency air-processed perovskite solar cells made in a humid atmosphere of 70% RH. Sol. RRL 1, 1700097.
Chu, Q.-Q. et al., 2018. Cost effective perovskite solar cells with a high efficiency and open-circuit voltage based on a perovskite-friendly carbon electrode. J. Mater. Chem. A 6, 8271–8279.
Cong, H. et al., 2017. Facile approach to preparing a vanadium oxide hydrate layer as a hole-transport layer for high-performance polymer solar cells.
ACS Appl. Mater. Interfaces 9, 18087–18094.
Conings, B. et al., 2015. Intrinsic thermal instability of methylammonium lead trihalide perovskite. Adv. Energy Mater. 5, 1500477.
Ding, J. et al., 2019. Fully air-bladed high-efficiency perovskite photovoltaics.
Joule 3, 402–416.
Domanski, K. et al., 2016. Not all that glitters is gold: metal-migration-induced degradation in perovskite solar cells. ACS Nano 10, 6306–6314.
Dou, B., Pool, V.L., Toney, M.F., van Hest, M.F.A.M., 2017. Radiative thermal annealing/in situ x-ray diffraction study of methylammonium lead triiodide: effect of antisolvent, humidity, annealing temperature profile, and film substrates. Chem. Mater. 29, 5931–5941.
Dualeh, A. et al., 2014. Effect of annealing temperature on film morphology of organic-inorganic hybrid perovskite solid-state solar cells. Adv. Funct.
Mater. 24, 3250–3258.
Eames, C. et al., 2015. Ionic transport in hybrid lead iodide perovskite solar cells. Nat. Commun. 6, 2–9.
Eperon, G.E. et al., 2014. Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells. Energy Environ.
Sci. 7, 982.
Eze, V.O., Mori, T., 2016. Enhanced photovoltaic performance of planar perovskite solar cells fabricated in ambient air by solvent annealing treatment method. Jpn. J. Appl. Phys. 55, 122301.
Guo, Q. et al., 2018. Low-temperature solution-processed vanadium oxide as hole transport layer for efficient and stable perovskite solar cells. Phys.
Chem. Chem. Phys. 20, 21746–21754.
128
Guo, T., Yun, S., Li, Y., Huang, A., Kang, L., 2020. Magnetron sputtered all- metal-oxide layers with balanced charge carrier transport efficiency for long-term stable perovskite solar cells. Sol. Energy 208, 652–658.
Han, T.-H. et al., 2019. Perovskite-polymer composite cross-linker approach for highly-stable and efficient perovskite solar cells. Nat. Commun. 10, 520.
Hong, S. et al., 2020. Direct observation of continuous networks of ‘sol–gel’
processed metal oxide thin film for organic and perovskite photovoltaic modules with long-term stability. J. Mater. Chem. A 8, 18659–18667.
Huang, Z., Wang, D., Wang, S., Zhang, T., 2018. Highly efficient and stable MAPbI3 perovskite solar cell induced by regulated nucleation and Ostwald recrystallization. Materials (Basel). 11, 778.
Icli, K.C., Ozenbas, M., 2018. Fully metal oxide charge selective layers for n-i- p perovskite solar cells employing nickel oxide nanoparticles.
Electrochim. Acta 263, 338–345.
Jena, A.K., Numata, Y., Ikegami, M., Miyasaka, T., 2018. Role of spiro- OMeTAD in performance deterioration of perovskite solar cells at high temperature and reuse of the perovskite films to avoid Pb-waste. J. Mater.
Chem. A 6, 2219–2230.
Jeon, M.-K., Ginting, R.T., Kang, J.-W., 2018. Impact of short-time annealing of methylammonium lead iodide on the performance of perovskite solar cells prepared under a high humidity condition. Mol. Cryst. Liq. Cryst.
660, 79–84.
Jiang, Q. et al., 2017. Enhanced electron extraction using SnO2 for high- efficiency planar-structure HC(NH2)2PbI3-based perovskite solar cells.
Nat. Energy 2, 16177.
Kato, Y. et al., 2015. Silver iodide formation in methyl ammonium lead iodide perovskite solar cells with silver top electrodes. Adv. Mater. Interfaces 2, 1500195.
Kim, J., Lee, Y., Yun, A.J., Gil, B., Park, B., 2019. Interfacial modification and defect passivation by the cross-linking interlayer for efficient and stable CuSCN-based perovskite solar cells. ACS Appl. Mater. Interfaces 11, 46818–46824.
Kim, M. et al., 2017. High-temperature–short-time annealing process for high- performance large-area perovskite solar cells. ACS Nano 11, 6057–6064.
129
Kim, M., Motti, S.G., Sorrentino, R., Petrozza, A., 2018. Enhanced solar cell stability by hygroscopic polymer passivation of metal halide perovskite thin film. Energy Environ. Sci. 11, 2609–2619.
Kim, S. et al., 2017. Relationship between ion migration and interfacial degradation of CH3NH3PbI3 perovskite solar cells under thermal conditions. Sci. Rep. 7, 1200.
Kim, W. et al., 2019. Enhanced long-term stability of perovskite solar cells by passivating grain boundary with polydimethylsiloxane (PDMS). J. Mater.
Chem. A 7, 20832–20839.
Kogo, A., Sanehira, Y., Numata, Y., Ikegami, M., Miyasaka, T., 2018.
Amorphous metal oxide blocking layers for highly efficient low- temperature brookite TiO2-based perovskite solar cells. ACS Appl. Mater.
Interfaces 10, 2224–2229.
Kojima, A., Teshima, K., Shirai, Y., Miyasaka, T., 2009. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J. Am. Chem.
Soc. 131, 6050–6051.
Kumar, C.V., Sfyri, G., Raptis, D., Stathatos, E., Lianos, P., 2015. Perovskite solar cell with low cost Cu-phthalocyanine as hole transporting material.
RSC Adv. 5, 3786–3791.
Lan, Y., Wang, Y., Song, Y., 2020. Efficient flexible perovskite solar cells based on a polymer additive. Flex. Print. Electron. 5, 014001.
Lee, J.-W., Kim, S.-G., Yang, J.-M., Yang, Y., Park, N.-G., 2019. Verification and mitigation of ion migration in perovskite solar cells. APL Mater. 7, 041111.
Lei, L. et al., 2019. Long-term stable perovskite solar cells with room temperature processed metal oxide carrier transporters. J. Mater. Chem.
A 7, 21085–21095.
Li, H. et al., 2019. High-efficiency and stable perovskite solar cells prepared using chlorobenzene/acetonitrile antisolvent. ACS Appl. Mater.
Interfaces 11, 34989–34996.
Li, J., Dong, Q., Li, N., Wang, L., 2017. Direct evidence of ion diffusion for the silver-electrode-induced thermal degradation of inverted perovskite solar cells. Adv. Energy Mater. 7, 1602922.
130
Li, N. et al., 2019. Sealing the domain boundaries and defects passivation by Poly(acrylic acid) for scalable blading of efficient perovskite solar cells.
J. Power Sources 426, 188–196.
Li, X. et al., 2018. In-situ cross-linking strategy for efficient and operationally stable methylammoniun lead iodide solar cells. Nat. Commun. 9, 3806.
Liu, L. et al., 2018. All-solution-processed perovskite light-emitting diodes with all metal oxide transport layers. Chem. Commun. 54, 13283–13286.
Liu, Z. et al., 2017. Nickel oxide nanoparticles for efficient hole transport in p- i-n and n-i-p perovskite solar cells. J. Mater. Chem. A 5, 6597–6605.
Lyashenko, D., Perez, A., Zakhidov, A., 2017. High-resolution patterning of organohalide lead perovskite pixels for photodetectors using orthogonal photolithography. Phys. status solidi 214, 1600302.
Mahmud, M.A. et al., 2017. Low temperature processed ZnO thin film as electron transport layer for efficient perovskite solar cells. Sol. Energy Mater. Sol. Cells 159, 251–264.
McKenna, B., Troughton, J.R., Watson, T.M., Evans, R.C., 2017. Enhancing the stability of organolead halide perovskite films through polymer encapsulation. RSC Adv. 7, 32942–32951.
Meng, Q. et al., 2020. Effect of temperature on the performance of perovskite solar cells. J. Mater. Sci. Mater. Electron.
Messegee, Z., Mamun, A. Al, Ava, T.T., Namkoong, G., Abdel-Fattah, T.M., 2019. Characterization of perovskite (CH3NH3PbI3) degradation with the integration of different polymers for increased stability. Mater. Lett. 236, 159–162.
Najafi, M. et al., 2018. Highly Efficient and Stable Flexible Perovskite Solar Cells with Metal Oxides Nanoparticle Charge Extraction Layers. Small 14, 1702775.
Nenashev, R.N., Mordvinova, N.E., Zlomanov, V.P., Kuznetsov, V.L., 2015.
Thermal decomposition of vanadyl acetylacetonate. Inorg. Mater. 51, 891–896.
Ouyang, D., Huang, Z., Choy, W.C.H.H., 2019. Solution-processed metal oxide nanocrystals as carrier transport layers in organic and perovskite solar cells. Adv. Funct. Mater. 29, 1804660.
131
Papadas, I.T., Galatopoulos, F., Armatas, G.S., Tessler, N., Choulis, S.A., 2019.
Nanoparticulate metal oxide top electrode interface modification improves the thermal stability of inverted perovskite photovoltaics.
Nanomaterials 9, 1616.
Peng, J. et al., 2018. A universal double-side passivation for high open-circuit voltage in perovskite solar cells: role of carbonyl groups in poly(methyl methacrylate). Adv. Energy Mater. 8, 1801208.
Qin, P.-L. et al., 2017. High-performance rigid and flexible perovskite solar cells with low-temperature solution-processable binary metal oxide hole- transporting materials. Sol. RRL 1, 1700058.
Raga, S.R., Jiang, Y., Ono, L.K., Qi, Y., 2017. Application of methylamine gas in fabricating organic–inorganic hybrid perovskite solar cells. Energy Technol. 5, 1750–1761.
Raiford, J.A. et al., 2019. Atomic layer deposition of vanadium oxide to reduce parasitic absorption and improve stability in n–i–p perovskite solar cells for tandems. Sustain. Energy Fuels 3, 1517–1525.
Reichardt, C., Welton, T., 2010. Solvents and solvent effects in organic chemistry. Wiley.
Shan, D. et al., 2019. The effect of decomposed PbI2 on microscopic mechanisms of scattering in CH3NH3PbI3 films. Nanoscale Res. Lett. 14, 208.
Shao, Y. et al., 2016. Grain boundary dominated ion migration in polycrystalline organic–inorganic halide perovskite films. Energy Environ. Sci. 9, 1752–1759.
Shen, H. et al., 2017. Improved reproducibility for perovskite solar cells with 1 cm2 active area by a modified two-step process. ACS Appl. Mater.
Interfaces 9, 5974–5981.
Song, Z. et al., 2015. Impact of processing temperature and composition on the formation of methylammonium lead iodide perovskites. Chem. Mater. 27, 4612–4619.
Song, Z., Watthage, S.C., Phillips, A.B., Heben, M.J., 2016. Pathways toward high-performance perovskite solar cells: review of recent advances in organo-metal halide perovskites for photovoltaic applications. J.
Photonics Energy 6, 022001.
132
Sun, H. et al., 2016. Low-temperature solution-processed p-type vanadium oxide for perovskite solar cells. Chem. Commun. 52, 8099–8102.
Supasai, T., Rujisamphan, N., Ullrich, K., Chemseddine, A., Dittrich, T., 2013.
Formation of a passivating CH3NH3PbI3/PbI2 interface during moderate heating of CH3NH3PbI3 layers. Appl. Phys. Lett. 103, 183906.
Tan, H. et al., 2017. Efficient and stable solution-processed planar perovskite solar cells via contact passivation. Science 355, 722–726.
Tan, Z. et al., 2012. Solution-processed vanadium oxide as a hole collection layer on an ITO electrode for high-performance polymer solar cells. Phys.
Chem. Chem. Phys. 14, 14589.
Tepliakova, M.M. et al., 2020. Incorporation of vanadium(V) oxide in hybrid hole transport layer enables long-term operational stability of perovskite solar cells. J. Phys. Chem. Lett. 11, 5563–5568.
Wang, D. et al., 2018. V2O5-PEDOT: PSS bilayer as hole transport layer for highly efficient and stable perovskite solar cells. Org. Electron. 53, 66–
73.
Wang, K. et al., 2015. Low-temperature and solution-processed amorphous WOx as electron-selective layer for perovskite solar cells. J. Phys. Chem.
Lett. 6, 755–759.
Wang, R. et al., 2019a. Caffeine improves the performance and thermal stability of perovskite solar cells. Joule 3, 1464–1477.
Wang, R. et al., 2019b. Constructive molecular configurations for surface- defect passivation of perovskite photovoltaics. Science 366, 1509–1513.
Wang, X. et al., 2017. Cerium oxide standing out as an electron transport layer for efficient and stable perovskite solar cells processed at low temperature. J. Mater. Chem. A 5, 1706–1712.
Wang, Y. et al., 2017. Stitching triple cation perovskite by a mixed anti-solvent process for high performance perovskite solar cells. Nano Energy 39, 616–625.
Xie, H. et al., 2019. Low temperature solution-derived TiO2-SnO2 bilayered electron transport layer for high performance perovskite solar cells. Appl.
Surf. Sci. 464, 700–707.
133
Yang, F. et al., 2018. Enhanced crystallization by methanol additive in antisolvent for achieving high-quality MAPbI3 perovskite films in humid atmosphere. ChemSusChem 11, 2348–2357.
Yang, F., Kang, D.-W., Kim, Y.-S., 2017. Improved interface of ZnO/CH3NH3PbI3 by a dynamic spin-coating process for efficient perovskite solar cells. RSC Adv. 7, 19030–19038.
Yang, H. et al., 2017. Effects of annealing conditions on mixed lead halide perovskite solar cells and their thermal stability investigation. Materials (Basel). 10, 837.
Yang, J. et al., 2019. All-inorganic perovskite solar cells based on CsPbIBr2 and metal oxide transport layers with improved stability. Nanomaterials 9, 1666.
Yang, J., Siempelkamp, B.D., Liu, D., Kelly, T.L., 2015. Investigation of CH3NH3PbI3 degradation rates and mechanisms in controlled humidity environments using in situ techniques. ACS Nano 9, 1955–1963.
You, J. et al., 2016. Improved air stability of perovskite solar cells via solution- processed metal oxide transport layers. Nat. Nanotechnol. 11, 75–81.
Yu, X., Qin, Y., Peng, Q., 2017. Probe decomposition of methylammonium lead iodide perovskite in N2 and O2 by in situ infrared spectroscopy. J. Phys.
Chem. A 121, 1169–1174.
Yuan, Y., Huang, J., 2016. Ion migration in organometal trihalide perovskite and its impact on photovoltaic efficiency and stability. Acc. Chem. Res.
49, 286–293.
Yuan, Z. et al., 2016. Approximately 800-nm-thick pinhole-free perovskite films via facile solvent retarding process for efficient planar solar cells.
ACS Appl. Mater. Interfaces 8, 34446–34454.
Yuan, Z. et al., 2015. Hot-electron injection in a sandwiched TiOx-Au-TiOx
structure for high-performance planar perovskite solar cells. Adv. Energy Mater. 5, 1500038.
Zhang, H. et al., 2017. Understanding the effect of delay time of solvent washing on the performances of perovskite solar cells. ACS Omega 2, 7666–7671.
Zhang, W. et al., 2020. Ethyl acetate green antisolvent process for high- performance planar low-temperature SnO2-based perovskite solar cells made in ambient air. Chem. Eng. J. 379, 122298.