Elsevier

Nano Energy

Volume 102, November 2022, 107695
Nano Energy

Back-contact perovskite solar cell fabrication via microsphere lithography

https://doi.org/10.1016/j.nanoen.2022.107695Get rights and content

Highlights

  • Efficient back-contact perovskite solar cell (BC-PSC) fabricated without the need for high-cost photolithography.

  • Highest stabilized PCE at 8.6% for a polycrystalline BC-PSC fabricated via a photolithography-free method.

  • Superior back-contact electrode morphology and smaller feature size using microsphere lithography.

  • Featuring device having the largest active area for a BC-PSC at 0.75 cm2.

  • In-depth charge-carrier dynamics analysis revealing charge extraction and interfacial properties in BC-PSC.

Abstract

Back-contact electrodes for hybrid organic-inorganic perovskite solar cells (PSCs) eliminate the parasitic absorption losses caused by the transparent conductive electrodes that are inherent to conventional sandwich-architecture devices. However, the fabrication methods for these unconventional architectures rely heavily on expensive photolithography, which limits scalability. Herein, we present an alternative cost-effective microfabrication technique in which the conventional photolithography process is replaced by microsphere lithography in which a close-packed polystyrene microsphere monolayer acts as the patterning mask for the honeycomb-shaped electrodes. A comprehensive comparison between photolithography and microsphere lithography fabrication techniques was conducted. Using microsphere lithography, we achieve highly efficient devices having a stabilized power conversion efficiency (PCE) of 8.6%, twice the reported value using photolithography. Microsphere lithography also enabled the fabrication of the largest back-contact PSC to date, having an active area of 0.75 cm2 and a stabilized PCE of 2.44%.

Graphical Abstract

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Low-cost and scalable microsphere lithography enables back-contact perovskite solar cells with a stabilized power output of 8.6%

Introduction

Hybrid organic-inorganic lead halide photo-absorbers have revolutionized the field of photovoltaics, leading to an unparalleled rate of development of perovskite solar cells (PSCs), which have recently achieved a power conversion efficiency (PCE) of 25.7% [1]. Currently, high efficiency PSCs can have either a p−i−n or n−i−p structure, in which the perovskite layer is located between the electron-transport and the hole-transport layers (ETL and HTL, respectively) and the electrodes. This “sandwich-type” PSC device architecture requires light to first pass through a transparent conductive electrode and ETL or HTL before reaching the perovskite photo-absorber, resulting in parasitic light absorption and reflection from these functional layers. As these optical losses are inherent to the sandwich-type structure, a new device architecture is required to fully realize the potential of PSCs to approach the Shockley–Queisser limit for single-junction solar cells [2].

Back-contact perovskite solar cells (BC-PSCs) employ an alternative device architecture, in which all electrodes and charge transport layers (CTLs) are located on the same side of the perovskite photo-absorber, thereby eliminating the optical losses that exist with sandwich-type PSCs. This structure also broadens the range of prospective materials for both the anode and cathode. Furthermore, the architecture of the pre-patterned anode and cathode in BC-PSCs precludes shunting path formation caused by pinholes in the perovskite layer, which is a common source of performance loss in sandwich-type devices [3]. Consolidating all the circuitry on one side of the device provides the additional benefit of simplifying interconnection and module assembly [4]. In the absence of the front electrodes, and with an optimized device design, optoelectronic modeling indicates that BC-PSCs ultimately offer superior photocurrent density compared with the conventional sandwich-type architecture [5], [6], [7].

A variety of back-contact electrode (BCE) architectures for PSCs have been designed, ranging from conventional co-planar interdigitated electrodes to more defect-tolerant quasi-interdigitated electrodes with finger and honeycomb structures [8], [9], [10], [11], [12], [13], [14], [15], [16]. The main challenge in electrode design is to ensure that both ETL and HTL are in close proximity to all points within the perovskite photo-absorber to maximize charge collection. Typical charge diffusion lengths in solution-processed polycrystalline perovskite films range from 100 nm to more than 6 µm, hence they require electrode feature sizes that are about 3 orders of magnitude smaller than those used in single crystalline Si-BC solar cells for efficient charge extraction [17], [18], [19], [20], [21], [22]. Unfortunately, the high resolution required for the BCE design for PSCs typically necessitates the use of photolithography, a time-consuming and expensive process that is not ideal for fabricating devices with a large active area. To overcome this issue, alternative methods need to be employed that permit low-cost, high-resolution, and high-throughput BCE fabrication.

The self-assembly of polystyrene (PS) microspheres has been used for scalable, photomask-free lithography in various applications [[23], [24], [25], [26]]. With careful control, PS microspheres form a compact monolayer having a honeycomb structure that resembles the pattern of a honeycomb-shaped quasi-interdigitated electrode (HQIDE) reported recently [12]. Previously, the Bach group demonstrated an electrostatic attraction-based method for PS monolayer assembly by attaching functionalized PS microspheres to a self-assembled monolayer (SAM) modified substrate, which yielded moderate microsphere coverage [27]. However, even with these modifications, the coverage and arrangement of PS microspheres on the substrate were still far from the ideal hexagonal close-packed (HCP) structure required for this method to act as a substitute for photolithography.

In this work, we report the use of microsphere lithography via a modified convective self-assembly technique with optimal PS microsphere coverage and arrangement. This technique allows for the fabrication of large-area BC-PSC devices without any modification to either the base substrate or the PS microspheres, thus addressing the cost and scalability issues associated with the photolithography process. A detailed comparison between BC-PSCs fabricated using microsphere lithography and photolithography was conducted. We also present results of a BC-PSC having the largest active area reported to date (0.75 cm2), further demonstrating the scalability of BC-PSCs using microsphere lithography.

Section snippets

Fabrication of back-contact electrodes via microsphere lithography

The fabrication process for a HQIDE by microsphere lithography (ML) is illustrated in Fig. 1a and is described in more detail in Methods. In brief, the process is as follows: 1) tin oxide (SnO2) is deposited as the ETL on an ITO-coated glass substrate; 2) a monolayer of close-packed polystyrene (PS) microspheres of 2.23 µm diameter is deposited via a modified convective self-assembly method following a previous work;[28] 3) the PS microspheres are etched via reactive ion etching (RIE) to reduce

Discussion

A photolithography-free technique employing modified convective self-assembly of polystyrene microspheres (microsphere lithography) was used to produce BC-PSCs having submicron features and improved electrode surface morphology. The reduction of electrode feature sizes and minimization of fabrication defects enabled the stabilized PCE of honeycomb-shaped BC-PSC to increase from 4.4% to a record high of 8.6%. Microsphere lithography was used to fabricate the largest BC-PSC reported to date,

Materials

Pre-patterned ITO glass substrates (7 Ω/sq) were purchased from Shenzhen Huayu Union Technology Co., Ltd.; Hellmanex™ III aqueous solution was purchased from Sigma-Aldrich; acetone (≥ 99.5%, CAS: 67–64–1) was purchased from Ajax Finechem; isopropanol (≥ 99.5%, CAS: 67–63–0) was purchased from EMPARTA® ACS; tin(IV) chloride pentahydrate (98%, CAS: 10026–06–9) was purchased from Thermo Fisher Scientific, Merck Pty. Ltd. and dissolved in anhydrous isopropanol (≥ 99.5%, Sigma-Aldrich) to make a

CRediT authorship contribution statement

Conceptualization, S.D., X.L. and U.B.; methodology, S.D., J.L., D.P.M., S.R.R., K.J.R., A.W., B.Z., N.H.V., X.L. and U.B.; formal analysis, S.D., B.T., A.S.R.C., Q.O., S.R.R., K.J.R., X.L. and U.B.; investigation, S.D., B.T., A.S.R.C., J.L., D.P.M., Q.O., A.D.S. and X.L.; writing – original draft, J.L., S.D.; writing – review and editing, S.D., B.T., A.S.R.C., D.P.M., A.D.S., S.R.R., K.J.R., X.L. and U.B.; visualization, S.D., A.S.R.C., A.D.S., X.L. and U.B.; supervision, A.S.R.C., X.L. and

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 Australian Government through the Australian Renewable Energy Agency (ARENA) the Australian Centre for Advanced Photovoltaics (ACAP) and the Australian Research Council (ARC, DE220100154). This work was performed in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). The authors acknowledge use of facilities within the Monash Centre for Electron Microscopy (MCEM). The

Siqi Deng is currently a PhD candidate in the department of Chemical and Biological Engineering at Monash University. He received Bachelor of Engineering (Honours) in Materials Science and Engineering from Central South University (China) and Monash University (Australia). His current research focuses on developing and characterizing back-contact perovskite photovoltaic devices.

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  • Siqi Deng is currently a PhD candidate in the department of Chemical and Biological Engineering at Monash University. He received Bachelor of Engineering (Honours) in Materials Science and Engineering from Central South University (China) and Monash University (Australia). His current research focuses on developing and characterizing back-contact perovskite photovoltaic devices.

    Boer Tan is currently a postdoctoral research fellow in the Department of Chemical and Biological Engineering, Monash University. She received her PhD from Monash University in 2020. Her research focuses on hole transporting layer modification and interfacial carrier dynamics in perovskite solar cells as well as the fabrication and characterization of back-contact perovskite solar cells.

    Anthony S. R. Chesman is a Principal Research Scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Group Leader of the Renewable Energy Systems Group. After completing his PhD in 2011 at Monash University on the magnetic properties of high nuclearity 3d/4f metal complexes, Dr Chesman moved into the field of renewable energy at CSIRO, with a particular focus on solar cells comprising earth-abundant materials. His current interests include solution-processed solar cell fabrication, the optical properties of optoelectronic devices, and translating next-generation energy systems to the marketplace.

    Jianfeng Lu is a professor at the Wuhan University of Technology, China. He received his Ph.D. from Huazhong University of Science and Technology working on porphyrin synthesis. Subsequently, he worked for 4 years as a postdoc at Monash University, Australia. In 2019, he returned to Wuhan University of Technology to establish his own research group. Prof Lu has a strong background in the area of photovoltaics and organic material synthesis. He is involved in fundamental and applied research in the area of perovskite solar cells and electrochromic devices.

    Dr. David P. McMeekin is currently a Marie Skłodowska-Curie Fellow at the University of Oxford. He was an Australian Center for Advanced Photovoltaics (ACAP) Fellow at Monash University. He holds a PhD in physics from the University of Oxford and received a M.Sc. degree in Microengineering from the Ecole Polytechnique de Lausanne (EPLF). His research interest is on integrating perovskite materials into tandem and multi-junction perovskites architectures for photovoltaic applications. He also specializes in finding perovskite compositions and methods that will increase the operational lifetime of devices for commercial applications.

    Qingdong Ou is an ARC DECRA Fellow at the Department of Materials Science and Engineering, Monash University, Australia. He received his PhD degree in Materials Science and Engineering from Monash University in 2019. He is an Associate Investigator of the ARC Centre of Excellence in Future Low-Energy Electronics Technology. Ou’s research involves the investigation of low-dimensional functional materials for nanophotonic and optoelectronic device applications.

    Andrew D. Scully is a Principal Research Scientist at CSIRO (Australia). After completing his Ph.D. at the University of Melbourne (Australia) using ultra-fast optical spectroscopy to probe super-efficient energy dissipation in UV-absorbing polymer stabilizers, he held post-doctoral positions at Kyoto Institute of Technology (Japan), University of Melbourne, and Imperial College London/Rutherford Appleton Laboratory (UK). At CSIRO he has led research into polymer-based active packaging materials utilizing novel photochemical and optical phenomena, biopolymer composites, and optical features for document security. His current research interests include the characterization of photo-physical and optoelectronic properties of printed photovoltaic films and the development of flexible barrier encapsulation.

    Dr. Sonia R. Raga received her B.Sc. (2010), M.Sc. (2011) and Ph.D. (2013) from Universitat Jaume I (Spain). She worked as a postdoctoral fellow at Okinawa Institute of Science and Technology (Japan, 2013–17) and at Monash University within the Australian Centre of Excellence in Exciton Science (2017–20). Dr. Raga is currently a laCaixa Junior Leader fellow at the Catalan Institute of Nanoscience and Nanotechnology (Spain). Her current research focuses on enhancing the perovskite solar cell stability and developing new lead-free metal halide photovoltaic materials for solar cells and photoelectrochemistry.

    Dr Kevin J. Rietwyk received his BSc (with honours)/BEd(sec) in 2009 and PhD in 2014 from La Trobe University, Australia. He worked as a postdoctoral researcher in the Zaban group (Israel) from 2014 to 2017 during which he was awarded a Marie Curie Individual Fellowship (2015–2017). From 2017–2022 he worked in the Udo Bach group at Monash University as a member of the Centre of Excellence in Exciton Science. His research interests are in advanced solar cell characterization techniques and high-throughput material discovery for contemporary photovoltaic applications.

    Anton Weissbach Born and raised in Dresden, Germany, Anton Weissbach has always been fascinated by scientific discoveries and inventions. He studied at the University of Bayreuth, Germany, and holds a bachelor's degree in Chemistry and a master's degree in Polymer Science. Focusing on functional materials and device engineering, he deepened his skillset during his stays at Heriot-Watt University, Edinburgh, UK and Monash University, Melbourne, Australia. Anton is now a PhD student at the Technical University Dresden, working on ion-electron conducting polymers and organic electrochemical transistors.

    Boya Zhao is a PhD student at the Department of Chemical and Biological Engineering, Monash University. He received his M.Sc. from the School of Chemical Engineering, Tianjin University in 2018. His research interests concentrate on back-contact perovskite photovoltaics and inorganic perovskite solar cells.

    Nicolas H. Voelcker completed his PhD at the DWI Leibniz Institute for Interactive Materials in 1999. After postdoctoral fellowships at the Scripps Research Institute, he became an academic at Flinders University rising to the rank of professor in 2008. In 2012, he became a professor in chemistry and materials science at the University of South Australia. From 2013–2015, he was Deputy Director of the Mawson Institute. Since 2017, he is the Director of the Melbourne Centre for Nanofabrication and a professor at the Monash Institute of Pharmaceutical Sciences at Monash University. His core research activity is the study of silicon-based nanostructures at biointerfaces.

    Yi-Bing Cheng is a Professor at Foshan Xianhu Laboratory and Wuhan University of Technology, China and Emeritus Professor of the Department of Materials Science and Engineering, Monash University, Australia. He specialises in inorganic materials. His current research interest is in perovskite solar cells and renewable hydrogen/ammonia production and applications.

    Xiongfeng Lin is currently a senior engineer in TCL Technology Group. He completed his Bachelor degree (with honours) at Central South University (China) and Monash University (Australia). He received his Ph.D. from Monash University working in the research group of Prof Udo Bach in 2019. His research interests focus on interfacial modification, back-contact perovskite photovoltaic devices and Cd-based QLEDs.

    Udo Bach is a full professor at Monash University, the Deputy Director of the ARC Centre of Excellence in Exciton Science and an ANFF-VIC Technology Fellow at the Melbourne Centre of Nanofabrication (MCN). He received his Ph.D. from the Swiss Federal Institute of Technology (EPFL, Switzerland) working in the research group of Prof Michael Grätzel. Subsequently he worked for 3 years in a technology start-up company in Dublin (Ireland) and spent 15 months as a postdoc in the group of Prof. Paul Alivisatos in UC Berkeley (USA) before moving to Monash University in November 2005 to establish his own research group. Prof Bach has a strong background in the area of photovoltaics and nanofabrication. He is involved in fundamental and applied research in the area of perovskite, dye-sensitized and plasmonic solar cells. He has additional research activities in the area of nanofabrication, DNA-directed self-assembly, nanoprinting, plasmonics for sensing and combinatorial photovoltaic materials discovery.

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