Research Article: Enhancing Efficiency and Stability of Photovoltaic Cells by Using Perovskite/Zr‐MOF Heterojunction Including Bilayer and Hybrid Structures

Date Published: January 01, 2019

Publisher: John Wiley and Sons Inc.

Author(s): Chia‐Chen Lee, Chih‐I Chen, Yu‐Te Liao, Kevin C.‐W. Wu, Chu‐Chen Chueh.

http://doi.org/10.1002/advs.201801715

Abstract

In this study, the effectiveness of using a perovskite/Zr‐metal–organic frameworks (MOFs) heterojunction in realizing efficient and stable inverted p–i–n perovskite solar cells (PVSCs) is demonstrated. Two types of Zr‐MOFs, UiO‐66 and MOF‐808, are investigated owing to their respectable moisture and chemical stabilities. The MOFs while serving as an interlayer in conjunction with the perovskite film are shown to possess the advantages of UV‐filtering capability and enhancing perovskite crystallinity. Consequently, the UiO‐66/MOF‐808‐modified PVSCs yield enhanced power conversion efficiencies (PCEs) of 17.01% and 16.55%, outperforming the control device (15.79%). While further utilizing a perovskite/Zr‐MOF hybrid heterojunction to fabricate the devices, the hybrid MOFs are found to possibly distribute over the perovskite grain boundary providing a grain‐locking effect to simultaneously passivate the defects and to reinforce the film’s robustness against moisture invasion. As a result, the PCEs of the UiO‐66/MOF‐808‐hybrid PVSCs are further enhanced to 18.01% and 17.81%, respectively. Besides, over 70% of the initial PCE is retained after being stored in air (25 °C and relative humidity of 60 ± 5%) for over 2 weeks, in contrast to the quick degradation observed for the control device. This study demonstrates the promising potential of using perovskite/MOF heterojunctions to fabricate efficient and stable PVSCs.

Partial Text

Organic–inorganic hybrid perovskite has recently attracted significant research attention in the photovoltaic community owing to its facile solution processability and exceptional optoelectronic properties.1, 2, 3, 4, 5, 6 In the past few years, remarkably semiconducting properties of the perovskite materials have been gradually identified, including intense wide‐range light‐harvesting, long carrier diffusion length, and tunable bandgaps, rendering them as an outstanding photovoltaic materials.7, 8, 9, 10 With these fundamental understandings, the power conversion efficiency (PCE) of perovskite solar cells has achieved an impressively rapid progress since its first debut in 2009.11 At present, the record PCE of perovskite solar cells (PVSCs) has reached 23.2% in this year.12, 13 This performance rivaling the value of the existing photovoltaic techniques shows great potential for commercialization due to its low‐cost and light‐weight advantages.14, 15

In summary, we herein described the effectiveness of perovskite/Zr‐MOF heterojunction, including bilayer architecture and the hybrid form, in fabricating high‐performance inverted p–i–n PVSCs. Two types of Zr‐MOFs, UiO‐66 and MOF‐808, were first employed as the surface modifier for the NiOx HTL in the device and were shown to enhance the crystallization of the perovskite film grown on top and simultaneously facilitate the charge‐extraction efficiency at the corresponding interface. Consequently, the UiO‐66/MOF‐808‐modified PVSCs could yield enhanced PCEs of 17.01% and 16.55%, outperforming the control device (15.79%). Moreover, we further exploited the perovskite/Zr‐MOF hybrid heterojunction to fabricate the devices. The hybrid MOFs were found to possibly distribute over the perovskite grain boundary, providing the grain‐locking effect. It not only passivates the defects but also reinforces the film’s robustness against the moisture invasion. The PCEs of the UiO‐66/MOF‐808‐hybrid PVSCs could be further enhanced to 18.01% and 17.81%, respectively. More intriguingly, over 70% of initial PCE can be retained after being stored in ambient air (25 °C and RH of 60 ± 5%) for over 2 weeks in contrast to the quick degradation observed for the control device. This study unravels the effectiveness of using perovskite/MOF heterojunction to fabricate efficient and stable solar cells, providing a new strategy for the future design of PVSCs.

Materials: The studied MOFs, UiO‐66 and MOF‐808, were prepared according to the procedures reported in the literature with slight modifications.25, 38 For synthesis of UiO‐66, zirconium tetrachloride (40 µmol) was dissolved in 5 mL of dimethylformamide (DMF) and BDC (40 µmol) was dissolved in 5 mL of DMF containing acetic acid (4.8 m). The zirconium tetrachloride‐containing DMF was poured into organic linker‐containing DMF solution in a Teflon container. The Teflon container was sealed in a Parr reactor and reacted at 120 °C for 8 h. The white UiO‐66 sample was spun down by centrifugation at 10 000 r.p.m for 10 min and washed with DMF for two times and methanol for three times. The as‐synthesized UiO‐66 was dried at 120 °C overnight to remove rest DMF before usage. For synthesis of MOF‐808, zirconyl chloride octahydrate (0.5 mmol) and BTC (0.5 mmol) were dissolved in a mixture containing 20 mL of DMF and 20 mL of formic acid. The solution was sealed in a glass vail at 100 °C for 7 days. The white MOF‐808 particles were collected by centrifugation and washed with DMF for one time. After that, the collected particles were suspended in solution to remove free linkers for six days. The solution was fresh DMF in first three days and replaced with anhydrous acetone in last three days. The as‐synthesized MOF‐808 was further dried at 150 °C for one day before usage.

The authors declare no conflict of interest.

 

Source:

http://doi.org/10.1002/advs.201801715

 

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