Elsevier

Current Applied Physics

Volume 19, Issue 12, December 2019, Pages 1427-1435
Current Applied Physics

Ultrasonically sprayed-on perovskite solar cells-effects of organic cation on defect formation of CH3NH3PbI3 films

https://doi.org/10.1016/j.cap.2019.09.010Get rights and content

Highlights

  • Fabrication of sequence sprayed-on perovskite layers was demonstrated.

  • An Urbach tail energy of the sprayed films depends significantly on the exposure time to the MAI.

  • PSCs with a sprayed-on approach showed the PCE of 10.09%.

Abstract

Methylammonium lead iodide (CH3NH3PbI3) based perovskite having low degrees of the disorder is of great interest for optoelectronic and photovoltaic applications. In this work, a layer of CH3NH3PbI3 was successfully prepared using an ultrasonically sprayed-nebulous method. Changes in structural and optical properties alongside with photo-induced charge separation and transportation behavior were systematically studied. The surface photovoltage spectra reveal a significant reduction of the density of deep defect states as the organic content was increased. It was observed that the measured values of Urbach energies decrease from 33.36 to 28.24 meV as the amount of organic content was increased to an optimum value. The best perovskite solar cells obtained using the sprayed-on approach exhibited a Jsc of 16.54 mA/cm2, a Voc of 0.99 V, and a FF of 62.4, resulting in an overall PCE of 10.09%.

Introduction

Recently methylammonium lead trihalide semiconducting material (CH3NH3PbX3, X = I, Cl, or Br) has received much attention in the research field of photovoltaics. This is due to its excellent optoelectronic properties such as a direct bandgap (~1.5 eV) [1], a long electron-hole diffusion length (1 μm) [2], low-exciton-binding energy [3,4], and a high charge carrier mobility [5]. In addition, the optical bandgap can be tuned by varying the composition of the halide anions. This last feature leads to light absorption over a broad range [6] making this class of materials suitable for use as the top cells in the narrow bandgap harvesters needed in the multi-junction solar cells based on silicon or on copper indium gallium selenide (CIGS) [[7], [8], [9]]. The new approach (using a perovskite-tandem system) has pushed up the power conversion efficiency (PCE) closer to the Shockley–Queisser limit [10]. Moreover, the superiority of the solution process ability makes it a more suitable pathway for the industrial production of perovskite solar cells (PSCs). This is attributed to a lower processing cost, more simplified device architectures [[11], [12], [13], [14]] and better surface/interface engineering techniques, all needed for achieving high-quality perovskite semiconducting films [[15], [16], [17]].

The best PCE reported so far has been limited to a small device area. Increasing the device area leads to a drastic drop in PCE [[18], [19], [20]]. The most prominent technique used for device fabrication has been the spin-casting method. However, this technique is non-scalable. In hopes of improving the throughput and scalability, a novel approach which is capable of producing high-quality perovskite films having the well-controlled thickness and large substrate area is studied and implemented. Typically, the perovskite active layers have been fabricated predominantly by an one-step deposition method in which both precursors in the appropriate stoichiometric amounts are mixed into in the same solution and then spin-coated into a thin film, and by a two-step deposition method or sequential deposition process, in which the two precursor solutions are prepared separately. One precursor usually lead iodide (PbI2) is deposited first, followed by the other, either by spin casting or immersion of the PbI2 spin-coated thin film into the next precursor solution methylammonium iodide (MAI) [21,22]. Recently, much effort has been made towards the production of high quality, and scalable perovskite layers. Some of the new techniques implemented are roll-to-roll printing [23], doctor blade coating [24], inkjet printing [25], vapor deposition [[26], [27], [28]], and spray deposition [29,30].

In this work, we report on a sequential sprayed nebulous deposition method. This approach has the potential to be scale-up the fabrication of the perovskite layer having full surface coverage within a controllable nitrogen environment. This involves the use of an ultrasonic vibrator to generate an ultra-fine aerosol of PbI2 and MAI. A layer of PbI2 was first deposited on the heated patterned (F-doped SnO2) FTO coated glass substrate by ultrasonic-sprayed technique, followed then by the deposition of atomized MAI, generated by the ultrasonic mist maker. This initiates a chemical reaction which results in the perovskite structure. In this manner, controllable reactions between PbI2 and MAI occur slowly. This allows for the tracking of precursor-to-perovskite transition at various stages of the reaction process. The evolution of the perovskite structure along with the changes in the optical properties, the photo-induced charge generation, and the charge separation behaviors were systematically investigated. This made it possible to gain insights into correlations between the structure-properties and the responses. This would help in the rational design of devices with optimal properties.

Section snippets

Sprayed-on CH3NH3PbI3

A layer of CH3NH3PbI3 perovskite was prepared by a sequentially sprayed nebulous deposition technique, the details of which are described elsewhere [31]. In brief, an ultrasonic generator was used to generate the precursor aerosols of PbI2 and MAI. A stream of the aerosolized precursor aerosols flowed towards the reaction zone using nitrogen gas (N2) as a carrier. The substrate holder, two inches in diameter, was attached to a heating source containing a thermocouple. A Kapton sheet was placed

Structural properties

Fig. 1(a) shows the XRD patterns of the sprayed-on CH3NH3PbI3 films at different time intervals. The structural evolution of the CH3NH3PbI3 structure concerning MAI spraying is observed. Initially, the solid-state complexes of PbI2 (sample with PbI2 layer only), reveal the characteristic central peak at 12.7° assigned to the reflection from the preferential orientation of (001) plane of PbI2. This peak by the crystallographic database (no.7–235), shows that the sprayed-on PbI2 layer has a

Conclusions

In conclusion, polycrystalline methylammonium lead iodide perovskite films were successively deposited on FTO coated glass substrate by an ultrasonic-sprayed nebulous deposition method. With this approach, a layer of PbI2 was first sprayed on the substrate then, sequentially by spraying the nebulized MAI. The amount of MAI content was investigated to have a crucial impact on the defect states during the evolution in the perovskite phase. Increasing the amount of MAI by varying the spraying

Conflicts of interest

The authors declare no conflicts to declare.

Acknowledgment

This work was supported by the Thailand Research Fund (MRG6282111), the co-funding from Electricity Generating Authority of Thailand (EGAT) and National Science and Technology Development Agency (NSTDA) (grant # P-17-51209), and by King Mongkut's University of Technology Thonburi through the “KMUTT through the Research Center of Excellent”. T.S is grateful to Kasetsart University Research and Development Institute (grant no.228.61 phase#2) for financial support.

References (63)

  • K. Tanaka et al.

    Solid State Commun.

    (2003)
  • H. Back et al.

    Sol. Energy Mater. Sol. Cells

    (2016)
  • M. Bag et al.

    Mater. Lett.

    (2016)
  • T. Miyasaka

    Chem. Lett.

    (2015)
  • S.D. Stranks et al.

    Science

    (2013)
  • K. Galkowski et al.

    Energy Environ. Sci.

    (2016)
  • C. Wehrenfennig et al.

    Energy Environ. Sci.

    (2014)
  • J.H. Noh et al.

    Nano Lett.

    (2013)
  • J.P. Mailoa et al.

    Appl. Phys. Lett.

    (2015)
  • J. Werner et al.

    J. Phys. Chem. Lett.

    (2016)
  • K.A. Bush et al.

    Nat. Energy

    (2017)
  • S. Foster et al.

    J. Appl. Phys.

    (2016)
  • J.M. Ball et al.

    Energy Environ. Sci.

    (2013)
  • H.J. Snaith

    J. Phys. Chem. Lett.

    (2013)
  • P. Docampo et al.

    Nat. Commun.

    (2013)
  • J. You et al.

    ACS Nano

    (2014)
  • M. Xiao et al.

    Angew. Chem. Int. Ed.

    (2014)
  • W. Nie et al.

    Science

    (2015)
  • J. You et al.

    Appl. Phys. Lett.

    (2014)
  • H.-S. Kim et al.

    Sci. Rep.

    (2012)
  • N.J. Jeon et al.

    Nature

    (2015)
  • The latest high efficiency was taken from NREL PV website at...
  • J. Burschka et al.

    Nature

    (2013)
  • J.-H. Im et al.

    Nat. Nanotechnol.

    (2014)
  • K. Hwang et al.

    Adv. Mater.

    (2015)
  • Y. Peng et al.

    RSC Adv.

    (2015)
  • M.M. Tavakoli et al.

    Sci. Rep.

    (2015)
  • G. Tong et al.

    RSC Adv.

    (2017)
  • A. Barrows et al.

    Energy Environ. Sci.

    (2014)
  • J.E. Bishop et al.

    Sci. Rep.

    (2017)
  • N. Henjongchom et al.

    Phys. Status Solidi

    (2018)
  • Cited by (4)

    • Tandem DSSC fabrication by controlled infiltration of organic dyes in mesoporous electrode using electric-field assisted spray technique

      2021, Solar Energy
      Citation Excerpt :

      In solar cells, the technique is widely used for deposition of the charge transport layers rather than the active material deposition and/or infiltration itself (Hong et al., 2010; Mehmood and Khan, 2019; Ponken et al., 2019). Spray deposition of the active absorber materials in solution-processable solar cells like perovskite, organic have been reported (Arumugam et al., 2018; Barrows et al., 2014; Henjongchom et al., 2019; Mohammad et al., 2019a; Waheed et al., 2020). In DSSCs, improvement in Jsc can be achieved by harvesting a greater portion of the incident light with increasing the dye-loading by increasing the thickness of the scaffolding layer (limited by carrier diffusion length of photo-anode) (Ngamsinlapasathian et al., 2005), incorporating plasmonic effect (suffers from the aggregation of plasmonic material and stability issues) (Joshi et al., 2017) or broadening the absorption spectrum by choosing suitable co-sensitizers (Çakar, 2019; Lan et al., 2012; Lee et al., 2008; Pinpithak et al., 2018; Rajkumar et al., 2019).

    View full text