Elsevier

Solar Energy

Volume 177, 1 January 2019, Pages 255-261
Solar Energy

Rapid and sheet-to-sheet slot-die coating manufacture of highly efficient perovskite solar cells processed under ambient air

https://doi.org/10.1016/j.solener.2018.11.020Get rights and content

Highlights

  • A rapid and nitrogen-free process for the fabrication of planar inverted structured perovskite solar cells (PSCs).

  • An alternative post-annealed method was developed by near-infrared (NIR) radiation to traditional heating oven. The annealed time can be shorten from 1500 s to 30 s by NIR irradiation.

  • The crystalline and nano-morphological structures of perovskite layers correlated to thermal and NIR annealing effects were revealed by the grazing-incidence wide-angle and small-angle X-ray scattering (GIWAXS and GISAXS).

  • Performance of sheet-to-sheet slot-die coated PSCs fabricated under ambient air can be achieved to 12.3%.

Abstract

A nitrogen-free and slot-die coating fabrication of perovskite solar cells combined with NIR annealing. We develop a fabrication approach of planar inverted structured perovskite solar cell (PSC) in ambient condition with a PCE of 12.4% as compared to that (13.3%) of PSC fabricated in glove box filled with nitrogen. In addition, we demonstrate an alternative post-annealed method by near-infrared (NIR) radiation to traditional heating method by oven. The annealed time by NIR can be shortened from 1500 s to 30 s and the device performance over 10% can be achieved. The present work investigates the NIR effect for different layers in the two-step processing on the cell performance. The grazing-incidence wide-angle and small-angle X-ray scattering (GIWAXS and GISAXS) techniques for the perovskite layers are performed to reveal the crystalline and nano-morphological structures of perovskite layers correlated to thermal and NIR annealing effects. Based on this approach under ambient air, we scale up to the large-area fabrication using the slot-die coating. The performance of slot-die coated PSC can achieve to 12.3%. The critical step is the control of PbI2 layer thickness. We also applied the NIR radiation to the slot-die coated PSC and the PCE of 11.4% can be achieved. Our study paves a facile way to rapid manufacture and mass production of perovskite solar cells.

Graphical abstract

Introduction

Organometal trihalide perovskite photovoltaic devices have recently drawn lots of attentions due to the properties of high absorption coefficient, broad absorption range, outstanding charge carriers mobility and long diffusion length (Stranks et al., 2013, Yu et al., 2017, De Wolf et al., 2014, Kagan et al., 1999). The power conversion efficiency (PCE) of the perovskite solar cells (PSCs) has significantly increased from 3.1% to 22.1% in these years (Yang et al., 2017). The hybrid perovskite photovoltaics were initially fabricated based on the device structure of the solid dye sensitized solar cells (DSSCs) (Kojima et al., 2009). Device performance by using DSSCs structure achieved several milestones (Yang et al., 2015, Jeon et al., 2015). These devices have the mesoporous TiO2 scaffold to support the perovskite materials. However, the mesoporous devices need a high temperature sintering that could increase the processing time and cost of mass-production. Recently, a simple and low cost planar heterojunction structure of perovskite solar cell has been developed without using mesoporous TiO2 scaffold. The first successful planar heterojunction structure can be traced back to the perovskite/fullerene structure reported by GuO, showing a PCE of 3.9% (Jeng et al., 2013). Recently, the PCE of the planar structure was pushed over 19% through perovskite film morphology control and interface engineering (Zhou et al., 2014). These results showed that the planar heterojunction structure can achieve similar device performance as the mesoporous structure. The planar structure can be divided into regular (n-i-p) and inverted (p-i-n) structure depending on which selective contact is used on the bottom. The p-i-n structure is derived from the organic solar cell. Several charge transport layers usually used in organic solar cells were successfully transferred into perovskite solar cells (You et al., 2014). The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and fullerene derivative were directly implemented as the hole transport layer (HTL) and electron transport layer (ETL) in the perovskite solar cells. Due to the choice of these materials, the inverted-structured perovskite devices showed the advantages of high efficiency, lower temperature processing and flexibility (You et al., 2014). For the frequently-used one-step preparation of perovskite materials, a solution containing CH3NH3I and lead halide salt (PbCl2, PbI2 and PbBr2) dissolved in N,N-dimethylformamide (DMF) is deposited onto the substrate. The deposited perovskite precursor layer was heated at the temperature over 100 °C for 10 ∼ 60 min to evaporate residual solvent from the film and also to control the crystallisation of the perovskite layer. The long heating time for the perovskite layer is a bottleneck to the mass-production or rapid manufacturing of perovskite solar cells. Moreover, the PCE of the perovskite solar cells is not stable after the devices are fabricated under ambient atmosphere due to the commercial requirements, such as low-cost and easy fabrication.

Perovskite films is the core of the performance of perovskite solar cells. The fabrication of the perovskite films can be divided into two kinds, one-step and two-step deposition approaches. Although the one-step deposition has been broadly used due to the simple process, the naturally crystallized perovskite film often exhibited an anisotropic growth, leading to low uniformity and poor coverage (Dualeh et al., 2014, Yantara et al., 2015). This low uniformity limited the perovskite solar cells to be applied to large-area mass-production. For the two-step deposition, PbI2 layers are firstly deposited on the substrate via various approaches to obtain the PbI2 layers with good uniformity and coverage. Hence, we think the two-step deposition is more suitable for mass-production process at the current status.

Due to the fast progress in PCE of perovskite solar cells, there have been a few investigations into the field of large-area PSC manufacture, such as doctor blading (Deng et al., 2015), spray coated (Das et al., 2015, Huang et al., 2016) and slot-die coating (Hwang et al., 2015, Cotella et al., 2017, Zuo et al., 2018, Kim et al., 2018). Among these approaches, slot-die coating process is deemed as a high throughput process with low materials waste, and is also a proven technique suitable for roll-to-roll process. Roll-to-roll compatible process for manufacturing PSCs has been proposed in recent years (Hwang et al., 2015, Cotella et al., 2017, Zuo et al., 2018, Kim et al., 2018, Qin et al., 2017, Ciro et al., 2017, Di Giacomo et al., 2018). The vacuum-free slot-die coated process was developed by using “gas-quenching” approach (Hwang et al., 2015, Qin et al., 2017), which is attached an additional slot-die head for high-pressure N2 gas to quickly dry the PbI2 film. This approach presents a facile way to form a good perovskite film by slot-die coating, however, the device area is only about 0.1 cm2 implies that it is not easy to manufacture a large-area film with high uniformity by controlling the N2 gas. The large-area PSCs module (>150 cm2) was performed in recent literature and the PCE of ∼12% can be achieved (Di Giacomo et al., 2018). This study demonstrates a great potential for the commercialization of PSCs, but the slot-die process was performed in the glove-box. Previous studies demonstrated that the additional humidity buffer or inert gas flow are needed for the perovskite fabrication due to the moisture sensitivity of perovskite films (Yang et al., 2017, Peiris et al., 2017, Zeng et al., 2017). For the two-step slot-die coating PSCs, the PCE of 14.7% can be achieved (Qin et al., 2017). However, these studies usually need longer annealing times (>10 min) to form uniform and dense perovskite films. This is still a limitation for the rapid mass-production process. Recently, some rapid light-based annealing strategies have been demonstrated for the efficient PSC fabrication. For instance, near-infrared annealing of a PSC based on the Al2O3 scaffold for 2.5 s achieved a PCE of 10.0% (Troughton et al., 2015). Other study utilized flash photonic annealing to heat perovskite films for 1.15 ms, and achieved the PCE of 11.3% (Troughton et al., 2016). However, these studies used the lab-scale spin coating process to fabricate the PSC, and mainly focus on the high-temperature-processed TiO2 to obtain good device performance.

Slot-die coating technique is proven to be a high throughput and low-cost process for the mass-production of PSCs. However, developing a rapid and facile way to fabricate large-area PSCs under ambient condition is still needed. In our previous studies, we have successfully applied the slot-die coating technique for printing large-area organic photovoltaics and modules (Huang et al., 2017, Huang et al., 2016). Therefore, we further employed the slot-die coating process in the fabrication of PSCs. For solving the mentioned problems toward commercialization of perovskite solar cell, we present an alternative method for annealing perovskite film which reduces the conventionally long annealing time to as less than 30 s whilst maintaining the PCE. This method adopted the commercially available near-infrared (NIR) radiation to rapidly cure the perovskite film. We also successfully developed a fabrication method of perovskite solar cell under ambient atmosphere (i.e., humid air of ∼R.H. 60% or more), which was based on the two-step processing. For fundamentally understanding, the synchrotron grazing-incidence wide-angle and small-angle X-ray scattering technique (GIWAXS/GISAXS) techniques were performed to investigate the hierarchical structure of perovskite crystalline films annealed by NIR and oven. The relationship between performance and structure are revealed. Finally, we combined the developed techniques with large-area fabrication of slot-die coating. The PbI2 layer thickness (concentration) in the two-step slot-die coating plays an important role for achieving high performance. The satisfying result would demonstrate this useful approach for the mass-production or commercialization of perovskite solar cells. Our work is the first study combining NIR annealing and the manufacture of slot-die coating PSCs based on low-temperature p-i-n structure. Our study not only provides the insight into the rapid annealing process of the low-temperature processed PSCs but also paves another facile way for the PSCs commercialization.

Section snippets

Experimental

For fabricating perovskite device as reference, the ITO-coated glass was successively ultrasonic cleaned for 30 min in deionized water, acetone and isopropanol, respectively. These substrates were then treated with nitrogen plasma cleaning for 10 min. The PEDOT:PSS HTL was spin-coated on the ITO-coated substrate at 5000 rpm for 30 s and was then annealed at 130 °C for 10 min. For deposited the perovskite active layer, a PbI2 precursor solution (1 M, 461 mg/ml) in DMF was prepared by stirring at

Results and discussion

In order to facilitate the manufacture the PSCs under atmosphere (/or humid air) condition, we firstly investigated the effect of atmosphere for different layers on the performance of PSCs. For the reference device, we spin coated the perovskite film via the mentioned two-step processing in a glove box filled with nitrogen. For PSCs fabricated with the atmosphere effect mentioned, we named the PSC with PbI2 layer (the first step) coated under air and the perovskite formation (the second step)

Conclusions

We have demonstrated that it is possible to manufacture perovskite solar cells with the high efficiency over 12% in ambient condition. In addition, we also show the NIR annealing process can be used for the rapid fabrication of perovskite solar cells as compared to the traditional method widely used in literature. Further optimization of NIR annealing parameters could certainly improve the PCE of the perovskite solar cell and lead to the possibility of rapidly processed and realize the

Acknowledgment

The authors would like to thank the financial support from the Ministry of Science and Technology of Taiwan (Gran No. 107-2218-E-131-007).

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