Formamidinium-incorporated Dion-Jacobson phase 2D perovskites for highly efficient and stable photovoltaics

doi:10.1016/j.jechem.2020.08.055

Journal of Energy Chemistry

Volume 57, June 2021, Pages 632-638

https://doi.org/10.1016/j.jechem.2020.08.055 Get rights and content

Highlights

•
Formamidinium (FA⁺) is introduced into Dion-Jacobson (DJ) phase 2D perovskites.
•
The FA-doped DJ 2D perovskite solar cells (PSCs) deliver a maximum PCE of 14.74%.
•
Unsealed PSCs are highly stable when exposed to heat, humidity and light radiation.

Abstract

Dion-Jacobson phase two-dimensional (DJ 2D) perovskites, recently attracting considerable interests, exhibit excellent environmental stability and structural tunability, but their solar cells still offer unsatisfactory power conversion efficiencies (PCEs). Herein, we develop DJ 2D perovskites employing formamidinium (FA⁺) as a ternary cation in the perovskite cages ((PDA)(FA)_x(MA)₃₋_xPb₄I₁₃, x = 0, 0.15, 0.3 and 0.6, PDA = 1,3-propanediammonium) for highly efficient and stable perovskite solar cells (PSCs). We found that the DJ 2D perovskite with a 10% FA⁺ fraction presents improved crystallinity, preferred vertical orientation, and longer charge carrier lifetime compared to that without FA⁺ doping. As a result, the FA-doped DJ 2D PSCs exhibit a champion PCE of 14.74% with superior device stability. The unencapsulated devices sustain over 92% of its initial PCE after storage at a constant relative humidity (RH) of 65% for 6000 h, 90% by heat at 85 °C in air for 800 h, and 94% under 1-sun illumination for 5000 h. These findings demonstrate that the incorporation of FA cation into the DJ 2D perovskite is a promising strategy to develop highly efficient and stable DJ 2D PSCs.

Graphical abstract

Formamidinium cation is incorporated into Dion-Jacobson phase two-dimensional layered perovskites used for perovskite solar cells, providing a best power conversion efficiency of 14.74% with excellent device stability.

Introduction

Stability issue has become a major challenge for the application of organic-inorganic hybrid halide perovskite solar cells (PSCs), although a power conversion efficiency (PCE) of over 25% has been already achieved [1], [2], [3], [4], [5], [6], [7]. Recently, two dimensional (2D) layered hybrid perovskites have emerged as alternatives to traditional 3D perovskites because of their higher environmental stability as well as structural diversity [8], [9], [10], [11], [12], [13], [14]. Among them, Ruddlesden-Popper (RP) phase 2D perovskites containing monoammonium cations have attracted considerable research interests, and efforts are made on optimizing crystal orientation and optoelectronic properties etc. to enhance the efficiency of RP 2D PSCs [11], [15], [16]. On the other hand, Dion-Jacobson (DJ) phase 2D perovskites, including divalent organic cations between inorganic perovskite layers, are a new class of 2D perovskites with even higher stability than RP analogues [2], [17]. DJ 2D PSCs based on 3-(aminomethyl)piperidinium (3-AMP) and its derived cations have been reported with PCEs from 7.34% to 9.2% and good device stability [18], [19]. Recently, we have developed ultrastable DJ 2D PSCs based on 1,3-propanediammonium (PDA²⁺) with a maximum PCE of 13.3% and proposed that the absence of van der Waals gaps plays a major role in the stability of such 2D perovskite materials [20]. Noted that in those works the inorganic layer number (n value) is smaller than 5, guaranteeing the high stability of the DJ 2D perovskites, which is the original intention of developing 2D perovskite materials. Although some DJ 2D PSCs such as those based on benzene dimethanammonium (BzAD) cation have been reported to provide a maximum PCE of 15.6%, the n value reaches 10, which is not beneficial for the device stability (20% of initial PCE lost after one week exposure to 20%–50% relative humidity (RH) under dark) [21]. Therefore, it is of critical significance to further increase the PCE of PSCs based on DJ 2D perovskites with small n values (such as n ≤ 4) in order to maintain enough material and device stability.

For this purpose, different attempts, such as film deposition techniques, cation/compositional engineering, and solvent engineering, have been made to further improve the PCE of DJ 2D PSCs having low n values. Among them, the compositional engineering approach, i.e. introducing additional cations such as formamidinium (FA⁺), can alter or eliminate unwanted crystal phases and enable control of the crystal quality. For example, Wu et al. and Ke et al. separately reported an FA-doped DJ 2D perovskite (3-AMP)(MA_0.75FA_0.25)₃Pb₄I₁₃ fabricated with different methods, delivering higher device efficiency and stability than the one without the introduction of FA⁺ [6], [22]. However, the PCE of such FA-doped DJ 2D PSCs is still lower than RP 2D and 3D counterparts, and their device stability needs to be further enhanced.

In this work, on the basis of highly stable PDA-based DJ 2D perovskites (PDA)(MA)₃Pb₄I₁₃ we previously reported, the FA⁺ is incorporated to partially replace the MA⁺ ((PDA)(FA)_x(MA)_3−xPb₄I₁₃, x = 0, 0.15, 0.3 and 0.6) to further improve the efficiency of DJ 2D PSCs. We found that by replacing 10% MA⁺ with FA⁺ the resultant FA-doped DJ 2D perovskite exhibits improved crystallinity, preferred crystal orientation, and prolonged charge carrier lifetime, boosting the device PCE from 13.28% to 14.74% under standard illumination. Moreover, the FA-doped DJ 2D PSCs are quite stable when subjected to a constant RH of 65% for 6000 h, heat at 85 °C for 800 h, and 1-sun light illumination for 5000 h.

Section snippets

Materials and methods

Formamidinium iodide (FAI, 98.99%, Sigma-Aldrich), lead iodide (PbI₂, 99%, Sigma-Aldrich), methylammonium iodide (MAI, 99.5%, Lumtec), 1,3-propanediamine (PDA, 98%, Inochem), γ-butyrolactone (GBL, 99%, Shanghai Bai Shun Biological Technology Co., Ltd.), dimethyl sulfoxide (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-Spirobifluorene (Spiro-OMeTAD, 99%, Borun New Material Technology Co., Ltd.), lithium bis(trifluoromethylsulfonyl)-imide (Li-TFSI, 99.95%, Sigma-Aldrich), and

Results and discussion

For the simplicity, the FA-based DJ 2D perovskites, (PDA)(FA)_x(MA)_3−xPb₄I₁₃ (x = 0, 0.15, 0.3 and 0.6), containing different FA⁺ ratios are denominated as FA-0, FA-5, FA-10, and FA-20, respectively, where the number next to FA represents the molar percentage of FA⁺ with respect to MA⁺. Their detailed preparation procedure is described in the Experimental section. First, we studied the UV–Vis absorption property of the FA-doped DJ 2D perovskites (Fig. 1a). The FA-0 film has an absorption onset

Conclusions

In summary, we have developed FA-doped DJ 2D perovskites, (PDA)(FA)_x(MA)_3−xPb₄I₁₃, with different ratios of FA⁺ for the application in DJ 2D PSCs. It is found that the DJ 2D perovskite film exhibits improved crystallinity and preferred vertical orientation as well as prolonged carrier lifetime when replacing 10% MA⁺ with FA⁺. Consequently, the FA-10-based DJ 2D PSC achieves a maximum PCE of 14.74%, higher than that obtained from devices without FA⁺ doping. More importantly, the FA-doped DJ 2D

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (No. 51973223), the DICP&QIBEBT UN201705, the Liaoning Revitalization Talents Program (XLYC1807231), and the DICP (Grant No. DICP I202011). The authors thank the Beamline BL14B1 at Shanghai Synchrotron Radiation Facility (SSRF) for providing the beam time.

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¹: These authors contributed equally to this work.

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Formamidinium-incorporated Dion-Jacobson phase 2D perovskites for highly efficient and stable photovoltaics

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Conclusions

Declaration of Competing Interest

Acknowledgments

Nano Lett.

Chinese Chem. Lett.

Joule

Sci. Bull.

J. Am. Chem. Soc.

J. Phys. Chem. Lett.

J. Mater. Chem. A

Sol. RRL

Energy Environ. Sci.

Angew. Chem. Int. Ed.

ChemSusChem

Adv. Mater.

Nature

J. Am. Chem. Soc.

Energy Environ. Sci

J. Am. Chem. Soc.