Controlling Thin Film Morphology Formation during Gas Quenching of Slot-Die Coated Perovskite Solar Modules

Abstract

Transferring record power conversion efficiency (PCE) >25% of spin coated perovskite solar cells (PSCs) from the laboratory scale to large-area photovoltaic modules requires significant advances in scalable fabrication techniques. In this work, we demonstrate the fundamental interrelation between drying dynamics of slot-die coated precursor solution thin films and the quality of resulting slot-die coated gas-quenched polycrystalline perovskite thin films. Well-defined drying conditions are established using a temperature-stabilized, movable table and a flow-controlled, oblique impinging slot nozzle purged with nitrogen. The accurately deposited solution thin film on the substrate is recorded by a tilted CCD camera, allowing for in situ monitoring of the perovskite thin film formation. With the tracking of crystallization dynamics during the drying process, we identify the critical process parameters needed for the design of optimal drying and gas quenching systems. In addition, defining different drying regimes, we derive practical slot jet adjustments preventing gas backflow and demonstrate large-area, homogeneous, and pinhole-free slot-die coated perovskite thin films that result in solar cells with PCEs of up to 18.6%. Our study reveals key interrelations of process parameters, e.g., the gas flow and drying velocity, and the exact crystallization position with the morphology formation of fabricated thin films, resulting in a homogeneous performance of corresponding 50 × 50 mm 2 solar minimodules (17.2%) with only minimal upscaling loss. In addition, we validate a previously developed model on the drying dynamics of perovskite thin films on small-area slot-die coated areas of ≥100 cm 2 . The study provides methodical guidelines for the design of future slot-die coating setups and establishes a step forward to a successful transfer of solution processes towards industrial-scale deposition systems beyond brute force optimization.

Modeling and Fundamental Dynamics of Vacuum, Gas, and Antisolvent Quenching for Scalable Perovskite Processes

“…In other words, all quenching processes share a common purpose: Reaching a very high supersaturation rate right at the moment when the critical concentration for perovskite nucleation is reached. Experimental evidence of this statement to be effective in predicting perovskite morphology formation was already provided by our previous works as well as those of other groups, [ 20,22,50–52 ] which is why we consider it a reasonable assumption herein. According to textbooks, [ 53 ] one possible definition of the supersaturation is $$$$\begin{equation}{\mathrm{\sigma}} = \ln \left( {C/{C}_0} \right)\end{equation}$$$$where C [mol m −3 ] is the molar solute concentration and C 0 [mol m −3 ] is the equilibrium molar concentration of solute (the concentration at which the material neither precipitates nor dissolves with time).…”

“…Experimentally, this is challenging to demonstrate if the wet film thickness is not constant. [ 52 ] In particular, since the MAPI solution dries very fast, optimal tuning will be very hard to control, causing the effective supersaturation rate much lower than reported above. In this context it is worth noting that the models can be used to predict (experimentally tested) process windows of high enough supersaturation, giving explicit guidelines to experimentalists.…”

“…[ 20 ] Furthermore, we directly observed the correlation between the position of the crystallization onset (determining the reachable supersaturation rate) and the morphology of slot‐die coated perovskite thin films. [ 52 ]…”

“…The higher the supersaturation rate, the more likely smooth perovskite films are achieved. [ 20,22,50–52 ] Depending on the exact crystallization dynamics (and all solution parameters that affect these), different thresholds in supersaturation rate may be needed. [ 69,70 ] In earlier works, [ 22 ] we showed that MAPI perovskite can crystallize in a smooth film when using static gas quenching.…”

Hybrid Two‐Step Inkjet‐Printed Perovskite Solar Cells

“…[4] Despite their high PCEs already demonstrated on a small scale, scalability to large-area solar cells remains a major challenge. [9] There are numerous approaches to the scalability of PSC fabrication, such as evaporation, [10,11] blade-coating, [12,13] slot-die-coating, [14] spray-coating, [15,16] or inkjet printing. [17] Among these technologies, inkjet printing is the only technique that enables free-form processing, [18] minimal material consumption, [19] and precise control of the amount of deposited material.…”