DEVELOPMENT OF ROLL-TO-ROLL SLOT DIE COATED PEROVSKITE SOLAR CELLS

Perovskite solar cells (PSCs) have gained a lot of attention in recent years because of their outstanding optoelectronic properties and ability to tolerate defects. Additionally, they can be produced at high throughput using solution processing techniques. It is this feature of perovskite that is leveraged in this work to show their scale up potential by R2R slot die coating.Slot die coating is a highly precise and controllable technique that can be used to coat a wide range of materials onto a variety of substrates, including flexible and rigid materials. Slot die coating is commonly used in the production of electronic devices, solar cells, and other products that require thin, uniform films of materials. First a P-I-N architecture of PSCs was developed and optimised with 4 layers slot die coated. This included the hole transport layer (PEDOT:PSS), active layer (MAPbI3), electron transport layer (PCBM), buffer layer (BCP). With 4 R2R slot die coated layer, a stabilised PCE of 12% is achieved. Further, a low toxic solvent system was used to coat the MAPbI3 and its economic benefits are discussed. Next, in efforts to replace PEDOT:PSS, PTAA hole transport layer was explored. Due to thin coating of PTAA on rough surfaces of PET-ITO, PTAA based devices resulted in high shorting. To avoid this a thin buffer layer of PEDOT:PSS on PET-ITO was slot die coated before coating PTAA. This improved the performance of the PSCs to 15.2%. Further, the role of PEDOT:PSS is characterised using AFM and XPS. Additionally, the optimization of a R2R slot die coating process for MAPbI3 was carried out on a PTAA surface. The loss of performance that occurred during the transfer from spin coating to R2R slot die coating was characterized, and multiple theories were tested to understand the cause. It was found that the poor interface between MAPbI3 and PTAA was responsible for the drop in performance. Finally, the addition of dimethyl sulfoxide (DMSO) helped to reduce the gap in performance between R2R and spin-coated MAPbI3 on PTAA hole transport layers. The presence of DMSO slowed the growth of crystal formation, leading to improved crystal orientation and improved performance of the PSCs

Predicting Low Toxicity and Scalable Solvent Systems for High‐Speed Roll‐to‐Roll Perovskite Manufacturing

Printed lead‐based perovskite photovoltaics (PV) have gained interest due to their potential to be manufactured with scalable roll‐to‐roll techniques. In industrial scale‐up, toxicity of inks can constrain roll‐to‐roll manufacturing due to the added cost of managing toxic effluents. Due to solvent toxicity, few perovskite solution chemistries in published works are scalable to gigawatt production capacity at low cost. Herein, it is shown that for scalable PV production, the use of aprotic polar solvents should be avoided due to their overall toxicity. Compliance with worldwide worker safety regulations for solvent exposure limits could require additional air handling requirements for some solvents, which in turn would affect cost‐effectiveness. It is shown that costs associated with handling of hazardous substances can be significant and estimate an added cost of ¢3.7/W for dimethylformamide (DMF)‐based inks. To solve this problem, a new perovskite ink solvent system is developed that is composed entirely of ether and alcohol, which has an effective exposure limit 14× higher than DMF, making it suitable for industrial coating processes. It is shown that the new ink solvent system is capable of fabricating high‐efficiency perovskite solar cells processed in 1 min on a standard roll‐to‐roll system

Predicting a process window for the roll-to-roll deposition of solvent-engineered SnO2 in perovskite solar cells

Lightweight flexible perovskite solar cells (PSCs) offer advantages over rigid solar cells including power to weight, variety of form factor and ability to scale. With breakthroughs in the power conversion efficiency (PCE) of PSCs, scaling up PSCs with similar performance has become a topic of interest. Roll-to-roll (R2R) manufacturing is one promising method to leverage the low temperature processing ability of PSCs. In this work, we demonstrate the R2R slot-die coating of the SnO2 electron transport layer, applying the low flow limit to showcase its pertinence in assessing the coating window for slot-die coating. It was observed that low flow limit can accurately predict the processing window for solvent-engineered SnO2 solutions streamlining scale up from benchtop to full R2R coating. We achieved a PCE of 16.35% for R2R-coated SnO2-based MAPbI3 perovskite devices exceeding the performance of benchtop-coated devices

Single-stage posterior-only debridement and transpedicular screw fixation for dorsolumbar tuberculosis: A prospective study of twenty cases

BACKGROUND: India bears the highest burden of tuberculosis (TB), i.e., about one-fourth of the total burden. Of the musculoskeletal TB, spinal TB affects half of the patients. Pharmacological treatment in the form of AKT is the mainstay of treatment of spinal TB, but surgery has its own role to play as an adjunct to AKT in selected cases. Various surgical methods and approaches are mentioned in literature. We studied the efficacy and safety of posterior only approach for decompression and internal fixation in treating thoracic and lumbar spinal TB in adults. MATERIALS AND METHODS: In this prospective randomized control study, we treated twenty patients with thoracic-lumbar TB with single-stage posterior only debridement, decompression, and transpedicular screw fixation. Preoperative and postoperative C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), kyphosis angle, visual analog scale (VAS) score and Frankel neurological grading, intraoperative blood loss, and duration of surgery were compared. Correction in kyphosis angle and loss of kyphosis angle at final follow-up was assessed. RESULTS: Sixteen male and four female patients with mean age 37.9 years were treated. Average follow-up was 14.95 months. Thirteen patients had two level involved; seven had single level. The average duration of surgery was 155 min (standard deviation [SD] 23.951). Preoperative average increase in ESR was 39.4 mm/h (SD 9.046) and 24.15 mm/h (SD 3.787) at 3 weeks. Average preoperative CRP was 15.7 mg/L (SD 5.398) and 9.05 mg/L (SD 3.456) at 3 weeks. Average preoperative kyphosis angle was 24.7° (SD 6.822) corrected to an average of 10.1° (SD 3.932) postoperative. At final follow-up, there was a mean loss of 1.4° of kyphosis angle. The average blood loss was 722.75 ml; the average duration of surgery was 228.5 min. The pain VAS dropped significantly from 7.05 (SD 1.468) to 3.9 (SD 1.209). At final follow-up, VAS was 1.7 (SD 0.864). All the patients had good neurological recovery except one. CONCLUSIONS: Single-stage posterior-only procedure is safe and effective for management of thoracolumbar spinal TB

Suppressing the δ-phase and photoinstability through a hypophosphorous acid additive in carbon-based mixed-cation perovskite solar cells

Despite a meteoric rise in the efficiency and promising scalability aspects, the operational stability of halide perovskites poses a serious concern for the commercialization of this technology. A paradigm shift from thermally unstable MA+ (methylammonium)-based perovskites to stable FA+ (formamidinium) and Cs+ (cesium)-based mixed halide perovskite variants is a step in this direction. However, phase stabilization of mixed-cation halide perovskites within a triple-layer scaffold remains a major challenge. In this work, we demonstrate two-step sequential fabrication of FA+- and Cs+-based halide perovskites with formulation Cs0.05FA0.95Pb(IBr)3 in a triple-mesoscopic scaffold with a carbon layer as the back electrode. A strong but reversible performance degradation is observed under light illumination. Addition of hypophosphorous acid (HPA) into the perovskite precursor solution improves the operational stability of the cells. A striking correlation between phase- and operational stability was observed. From structural analysis, it was found that HPA tends to suppress the formation of a hexagonal yellow phase and promotes trigonal black phase formation. Further optical analysis of the cells showed the improvement in the optoelectronic properties in terms of defects and carrier recombination in the perovskite formed by HPA addition supported by external quantum efficiency and photoluminescence measurements. A stable 12% power conversion efficiency was achieved by tuning the composition and optimizing the process conditions for Cs0.05FA0.95Pb(IBr)3-based triple-mesoscopic perovskite solar cells.National Research Foundation (NRF)N.M. and S.G.M. would like to acknowledge funding from the Singapore National Research Foundation through the IntraCREATE Collaborative Grant (NRF2018-ITC001-001) and the Competitive Research Program: NRF-CRP14-2014-03