Large-scale full-solution, vacuum-free gravure printed ITO-free flexible organic solar cells

Table of Contents

1 Introduction

1.1 The need for solar energy

1.2 Generations of solar cell technology

1.3 Research fields of organic solar cells

2 State of art and motivation

3 Fundamentals

3.1 Working principle of OPV device

3.2 Device geometries of OPV device

3.3 ITO-free OPV device

3.4 Materials in OPV device

3.5 Characterization of OPV device

3.5.1 J-V curve

3.5.2 LBIC

3.6 Large-scale manufacturing methods for OPV

3.6.1 Coating technologies

3.6.1.1 Slot-die coating

3.6.1.2 Blade coating

3.6.1.3 Spray coating

3.6.2 Printing technologies

3.6.2.1 Screen printing

3.6.2.2 Gravure printing

3.6.2.3 Flexographic printing

3.6.2.4 Inkjet printing

3.6.3 Summary of coating and printing techniques

3.6.4 R2R concept and manufacturing strategies

4 Experimental

4.1 Gravure printing of silver back cathode

4.2 Gravure printing of ZnO

4.3 Gravure printing of active layer

4.4 Gravure printing of PEDOT:PSS

4.5 Gravure printing of silver front anode

4.6 Deposition of remaining layers

4.7 Characterization

5 Results and discussion

5.1 Gravure printed silver back cathode

5.2 Gravure printed ZnO

5.3 Gravure printed active layer

5.4 Gravure printed PEDOT:PSS

5.5 Gravure printed silver front anode

5.6 Summary of results

6 Challenges

7 Conclusion and outlook

Research Objectives and Core Themes

The primary objective of this thesis is to perform a feasibility study on the fabrication of large-scale, fully solution-processed, vacuum-free, and ITO-free flexible organic solar cells using gravure printing. The study aims to transition from lab-scale production to large-area roll-to-roll (R2R) manufacturing, addressing challenges in printing uniformity, material wetting, and device architecture.

• Manufacturing of large-scale ITO-free flexible organic solar cells.
• Evaluation of gravure printing as a full-solution production technique.
• Analysis of material compatibility and layer morphology in roll-to-roll processing.
• Investigation of printing parameters and their impact on device performance and homogeneity.
• Comparison of different coating and printing strategies for R2R optimization.

Excerpt from the Book

Chapter Summaries

1 Introduction: Provides a rationale for renewable energy and solar power while outlining the three generations of solar cell technologies and the focus on organic solar cells.

2 State of art and motivation: Reviews existing literature on gravure-printed OPV components and establishes the goal of fabricating fully gravure-printed, ITO-free flexible solar cells.

3 Fundamentals: Details the operational principles of BHJ devices, material selections, characterization techniques like J-V and LBIC, and large-scale manufacturing methods.

4 Experimental: Describes the chronological fabrication process of the ITO-free inverted layer stack, including machinery setup, ink properties, and deposition parameters.

5 Results and discussion: Analyzes the printing quality of individual layers, discusses morphological defects like viscous fingering, and presents performance data for completed test cells.

6 Challenges: Identifies technical bottlenecks encountered during R2R gravure printing, such as layer wetting issues, alignment difficulties, and the impact of the discrete manufacturing route.

7 Conclusion and outlook: Summarizes the key findings regarding the feasibility of full-scale gravure printing and suggests future research directions to improve performance and stability.

Keywords

Organic Photovoltaics, Gravure Printing, Roll-to-Roll Processing, ITO-free, Flexible Solar Cells, Bulk Heterojunction, P3HT:PCBM, PEDOT:PSS, Device Geometry, Printing Uniformity, Large-scale Manufacturing, Viscous Fingering, Surface Energy, Layer Deposition.

Frequently Asked Questions

What is the primary focus of this thesis?

The thesis focuses on the feasibility of manufacturing fully solution-processed, vacuum-free, and ITO-free flexible organic solar cells using large-scale gravure printing techniques.

Which type of solar cell technology is investigated?

The research investigates third-generation polymer solar cells, specifically utilizing the bulk heterojunction (BHJ) principle with P3HT:PCBM active layers.

What is the main research question or goal?

The goal is to demonstrate that all layers of an inverted OPV device can be gravure-printed at scale, aiming to replace vacuum-based and ITO-dependent processes with a high-throughput, roll-to-roll (R2R) production method.

What scientific methods were used to evaluate the devices?

The study primarily used Current Density-Voltage (J-V) characterization to measure power conversion efficiency and Light Beam Induced Current (LBIC) to visualize active area coverage and identify morphological defects like viscous fingering.

What are the major challenges addressed in the work?

Key challenges include layer wetting and dewetting issues, achieving uniform layer thickness during printing, managing side registration of the substrate, and the limitations of the discrete manufacturing process compared to an ideal inline workflow.

Which keywords characterize this research?

The research is characterized by terms such as Organic Photovoltaics, Gravure Printing, Roll-to-Roll Processing, ITO-free, and Flexible Solar Cells.

Why was the "IOne" stack chosen for this study?

The IOne stack was chosen because it allows for an ITO-free architecture by using silver grids and PEDOT:PSS, which is better suited for full-solution, large-scale production compared to standard glass/ITO substrates.

How does the "viscous fingering" effect impact the solar cells?

Viscous fingering results in non-uniform, streaky layers with varying thicknesses, which leads to inhomogeneous electrical current generation, as visualized by LBIC imaging, and contributes to lower overall power conversion efficiency.