Flexible perovskite solar cells (f‐PSCs) have attracted great attention due to their promising commercial prospects. However, the performance of f‐PSCs is generally worse than that of their rigid counterparts. Herein, it is found that the unsatisfactory performance of planar heterojunction (PHJ) f‐PSCs can be attributed to the undesirable morphology of electron transport layer (ETL), which results from the rough surface of the flexible substrate. Precise control over the thickness and morphology of ETL tin dioxide (SnO2) not only reduces the reflectance of the indium tin oxide (ITO) on polyethylene 2,6‐naphthalate (PEN) substrate and enhances photon collection, but also decreases the trap‐state densities of perovskite films and the charge transfer resistance, leading to a great enhancement of device performance. Consequently, the f‐PSCs, with a structure of PEN/ITO/SnO2/perovskite/Spiro‐OMeTAD/Ag, exhibit a power conversion efficiency (PCE) up to 19.51% and a steady output of 19.01%. Furthermore, the f‐PSCs show a robust bending resistance and maintain about 95% of initial PCE after 6000 bending cycles at a bending radius of 8 mm, and they present an outstanding long‐term stability and retain about 90% of the initial performance after >1000 h storage in air (10% relative humidity) without encapsulation.
It is highly desirable to develop large‐scale, low‐cost fabrication processes for flexible perovskite solar cells (f‐PSCs) under ambient conditions for accelerating their potential commercialization. Roll‐to‐roll (R2R) printing technology enables high‐output manufacturing and is well suited for commercially processing f‐PSCs. Herein, triple‐cation f‐PSCs are developed with a planar heterojunction structure consisting of polyethylene‐2,6‐naphthalate/indium tin oxide/SnO2/perovskite/spiro‐OMeTAD/Ag via a combination of R2R microgravure printing and slot‐die coating under ambient conditions with a relative humidity of ≈40%. A mixture of isopropanol and water is used to dilute an as‐purchased SnO2 colloid solution and modify the contact between the electron‐transport layer (ETL) and substrate, leading to a smooth morphology of the R2R‐printed ETL SnO2 layer. Furthermore, suitable intrinsic organic salt additives and the N2 gas blowing‐assisted process are introduced to effectively improve the crystallization of the perovskite, resulting in a high‐quality perovskite film via R2R. After the optimization, the f‐PSCs based on the R2R‐printed ETL SnO2 and the perovskite film under an ambient condition show a power conversion efficiency (PCE) of up to 10.56% and an average PCE of 9.97%. This study provides a potential strategy for commercially fabricating f‐PSCs via a scalable and efficient R2R printing process.
Perovskite solar cells (PSCs) have attracted tremendous attention as a promising alternative candidate for clean energy generation. Many attempts have been made with various deposition techniques to scale-up manufacturing. Slot-die coating is a robust and facile deposition technique that can be applied in large-area roll-to-roll (R2R) fabrication of thin film solar cells with the advantages of high material utilization, low cost and high throughput. Herein, we demonstrate the encouraging result of PSCs prepared by slot-die coating under ambient environment using a two-step sequential process whereby PbI2:CsI is slot-die coated first followed by a subsequent slot-die coating of organic cations containing solution. A porous PbI2:CsI film can promote the rapid and complete transformation into perovskite film. The crystallinity and morphology of perovskite films are significantly improved by optimizing nitrogen blowing and controlling substrate temperature. A power conversion efficiency (PCE) of 18.13% is achieved, which is promising for PSCs fabricated by two-step fully slot-die-coated devices. Furthermore, PSCs with a 1 cm2 area yield a champion PCE of 15.10%. Moreover, a PCE of 13.00% is obtained on a flexible substrate by the roll-to-roll (R2R) coating, which is one of the highest reported cells with all layers except for metal electrode fabricated by R2R process under ambient condition.
The power conversion efficiency of perovskite solar cells (PSCs) has recently reached 24.2% [1], the threshold for serious commercial interest, triggering an intense search for prospective large-scale production methods that will enable a swift transition from the laboratory to industrial-scale manufacture. Several industrially-compatible scalable methods have been deployed to fabricate PSCs, but the efficiencies of devices prepared using these methods remain inferior to devices prepared in the laboratory using spin coating, a technique that is unsuitable for large-scale manufacturing. A key challenge for the successful commercialization of PSCs is the production of highly uniform, pinholefree films over a sufficiently large area while also controlling the crystallization process. Researchers in private and public sector organizations are devoting tremendous effort to overcoming these hurdles. Among the reported scalable methods, use of slot-die coating in sheet-to-sheet (S2S, batch) or roll-toroll (R2R, continuous) processes is attractive for large-scale, low-cost manufacturing of PSCs, particularly on flexible substrates. In this review, we summarize recent advances in low-temperature S2S and R2R slot-die coating processes for PSCs, outline the key processing parameters controlling PSC fabrication and their impact on device performance, and describe current challenges and future prospects.
Flexible solar cells are promising for space applications due to their unique properties including lightweight and flexibility. In particular, flexible perovskite solar cells (f-PSCs) with high efficiencies have a much stronger competitiveness, but study about the radiation tolerance of f-PSCs is still absent. Herein, the radiation tolerance of methylammonium (MA)/formamidinium (FA)/cesium (Cs)-based triple cation f-PSCs under γ-ray was investigated systematically, with a planar heterojunction structure of PEN/ ITO/SnO 2 /perovskite/spiro-OMeTAD/Ag. The results show that the photovoltaic performance of the cells experienced an obvious deterioration after γ-ray irradiation, especially the short-circuit current density. It is mainly attributed to the decreased transparency of the flexible substrate, namely, poly(ethylene naphthalate) (PEN), and the decomposition of perovskite films under γ-ray irradiation. In spite of the performance degradation, the radiation tolerance of f-PSCs was still much better than that of rigid counterparts. It suggests that f-PSCs are more suitable for space application, showing better prospects.
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