Fabrication of High Efficiency Perovskite Solar Cells through the Roll-to-Roll Compatible Slot Die Coating with Highly Reliable Simultaneous Multi Assisting System

Abstract

Perovskite solar cells (PeSCs) have been receiving significant attention from research society and industry of solar cells in the last few years. The power conversion efficiency (PCE) of perovskite photovoltaics has reached over 24% from research cells fabricated by spin coating. Current record efficiency is high enough for commercial applications, however, technical status of upscaling has been at very early stage. Most of demonstrations of scalable processes reported to date have been performed under strictly controlled processing environment with extremely low humidity or N2 gas in glove box. Though keeping manufacturing line under dry conditions is technically possible, controlling ambient conditions will add to manufacturing costs. Therefore, if the process is tolerant to variations in the environmental conditions, it would be ideal. In this thesis, it is focused that investigation and demonstration of roll-to-roll compatible coating and improving reliability of processing at ambient manufacturing environment using polymer additives. Chapter 1 provides a general introduction and fundamentals to solar cells and scalable fabrication methods of organic-inorganic hybrid perovskite solar cells. In Chapter 2, CH3NH3PbI3-based planar perovskite solar cells were fabricated by slot-die coating, a scalable method. Slot-die coating tends to produce perovskite layers with much lower coverage with overgrown crystals than spin coating, which does not include a self-drying mechanism in the process. To mimic the self-drying behavior inherent in spin coating, the present study introduces a blowing step in the slot-die coating method, which significantly improved coverage of the prepared slot-die coated perovskite films. The slot-die-coated device with blowing showed a moderate power conversion efficiency (PCE) of 8.8 %. The morphology of the slot-die-coated perovskite film is further improved by optimizing the deposition temperature. The combination of blowing and heating during the slot-die-coating step and the introduction of a printing-friendly hole transport layer resulted in a PCE of 12.7 % for the devices fabricated in air. In Chapter 3, heating-assisted deposition is an industry-friendly scalable deposition method. This work used this manufacturing method with a slot die coating to fabricate perovskite solar cells via a roll-to-roll process. Here, the feasibility of the method has been demonstrated after initial testing on a rigid substrate using a benchtop slot die coater in air. The fabricated solar cells exhibited power conversion efficiencies reaching 14.7%. A non-electroactive polymer additive was used with the perovskite formulation and was found to significantly improve the humidity tolerance. These deposition parameters were also used in the roll-to-roll setup. The perovskite layer and the other solution-processed layers were slot die coated, and the device shows power conversion efficiencies ranging up to 11.7%, which is the highest efficiency obtained from fully roll-to-roll processed perovskite solar cells.