Roll-to-roll gravure-printed flexible perovskite solar cells using eco-friendly antisolvent bathing with wide processing window

Abstract

Driven by recent improvements in efficiency and stability of perovskite solar cells (PSCs), upscaling of PSCs has come to be regarded as the next step. Specifically, a high-throughput, low-cost roll-to-roll (R2R) processes would be a breakthrough to realize the commercialization of PSCs, with uniform formation of precursor wet film and complete conversion to perovskite phase via R2R-compatible processes necessary to accomplish this goal. Herein, we demonstrate the pilot-scale, fully R2R manufacturing of all the layers except for electrodes in PSCs. Tert-butyl alcohol (tBuOH) is introduced as an eco-friendly antisolvent with a wide processing window. Highly crystalline, uniform formamidinium (FA)-based perovskite formation via tBuOH:EA bathing was confirmed by achieving high power conversion efficiencies (PCEs) of 23.5% for glass-based spin-coated PSCs, and 19.1% for gravure-printed flexible PSCs. As an extended work, R2R gravure-printing and tBuOH:EA bathing resulted in the highest PCE reported for R2R-processed PSCs, 16.7% for PSCs with R2R-processed SnO₂/FA-perovskite, and 13.8% for fully R2R-produced PSCs.

Fig. 1. Formation of high-quality perovskite layers via antisolvent bathing.

a Schematic diagram representing R2R processing of perovskite layer. Each step of processing, considerations of each step, and timescales are presented in the figure. b Photographs of perovskite film after bathing in various antisolvents. The images were recorded as a video and captured at certain times. Final films were obtained by thermal annealing of the intermediate film after bathing for 20 s.

Fig. 2. Characterization of perovskite layers formed by bathing in various antisolvent.

a XRD spectra of perovskite films obtained by bathing in various antisolvents. b SEM image of the perovskite film made by bathing in tBuOH:EA. c Grain size distribution curves for perovskite films fabricated with various antisolvents. d Champion PCE of PSCs fabricated by bathing in various antisolvents.

Fig. 3. Processing window of perovskite formation processes via antisolvent bathing and champion device performance.

a Average (bar) and champion PCE (circle) of PSCs made by bathing in antisolvents according to amounts of DMSO in the precursor solution with respect to the amount of perovskite. The gray error bars indicate standard deviation of PCEs. b PCE of tBuOH:EA derived PSCs depending on spin-coating duration. c PCE of PSCs fabricated by tBuOH:EA bathing for controlled time. In both figures, indigo dots represent average PCEs, bars indicate standard deviations, and small purple dots mean champion PCEs. d Current density-voltage (J-V) curves of champion devices fabricated by bathing in tBuOH:EA. Average PCE values were obtained from at least 12 devices for each condition.

Fig. 4. Table-top gravure-printing of multi-cation flexible PSCs.

a Schematic illustration of table-top gravure printing. b SEM image of perovskite film fabricated by table-top gravure printing and subsequent bathing in tBuOH:EA. c Cross-sectional SEM image of flexible PSCs made by table-top gravure printing. Each layer was colored differently to distinguish it from the others. FAPbI₃ indicates (FAPbI₃)_0.95(MAPbBr₃)_0.05. (inset) Diagram illustrating the structure of device used in this study. d Representative J-V curves of gravure-printed PSCs with Spiro-OMeTAD. Spiro-OMeTAD was deposited by spin-coating (indigo), shear-coating (purple) or gravure-printing (salmon). e A J-V curve of champion device fabricated by gravure-printing. f Efficiency of the champion devices measured by MPPT technique.

Fig. 5. Modulation of perovskite inks and impact on the resolution of gravure-printed pattern.

a Viscosity of perovskite precursor solutions having different concentrations. Images of (b) printing plate and (c) printed perovskite patterns on PET substrate with different concentrations.

Fig. 6. Fully R2R gravure printing of PSCs except electrodes.

a Diagram showing R2R processing for the fabrication of flexible PSCs. b Photograph of fully R2R-processed PSCs. (inset) Image of a R2R-processed roll showing constituent layers of PSCs after removing each layer manually. c Cross-sectional SEM image of fully R2R printed PSCs. Each layer was given a different color. d J-V curves of champion device made from R2R-processed SnO₂/perovskite and Spiro-OMeTAD (shear-coating: purple, spin-coating: indigo). e The J-V curves of fully R2R gravure-printed PSCs. FAPbI₃ denotes (FAPbI₃)_0.95(MAPbBr₃)_0.05.