Improving the performance and reliability of perovskite solar cells using scalable deposition methods for the roll-to-roll system
Creators: name: Benitez Rodriguez, Juan
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340301
subject: Inorganic materials (incl. nanomaterials)
classificationCode: 340305
subject: Physical properties of materials
classificationCode: 401605
subject: Functional materials

description: Organic-inorganic metal halide perovskite materials have received substantial attention in the photovoltaics field due to their compatibility with solution processing and the substantial power conversion efficiencies (PCEs) of &gt;25% obtained in perovskite solar cells (PSCs). These high PCE values are comparable to those achieved by well-established photovoltaic technologies such as crystalline silicon and CdTe, and relate to high absorption coefficients, long charge carrier diffusion lengths and tunability in energy band gaps of the halide perovskite materials. Nevertheless, the main challenges for PSCs are the improvement of large-area processing homogeneity and lifetime. PSC stability is affected by a wide range of parameters, including exposure to visible and UV light, high temperature, oxygen, humidity, and electrical bias. 

Thus, the fabrication of PSCs using formamidinium (FA) and caesium (Cs) cations, which present higher stability to environmental conditions than methylammonium (MA) only perovskite films, was investigated using scalable approaches. A nitrogen gas flow was applied to promote perovskite nucleation and crystallization, achieving high quality FA0.91Cs0.09PbI3 (FA-Cs) films using either spin-coating or slot-die coating under ambient conditions. The addition of Cs and MACl reduced the temperature required for the formation of the desirable α-phase perovskite structure to below 160 °C. This lower temperature is crucial for the fabrication of flexible perovskite solar cells (f-PSCs) due to the temperature processing limitations of the flexible substrates used, such as polyethylene terephthalate (PET). The nitrogen gas flow was also applied in a roll-to-roll (R2R) system for the fabrication of f-PSCs.

The PSCs fabricated under ambient conditions (40-50% relative humidity (RH)) using spin coated devices presented PCEs up to 19%, whereas slot-die coated perovskite films or R2R for f-PSCs presented PCEs up to 17 or 15%, respectively, for PSCs with an active area of 0.2 cm2. A fluorinated cation additive, 2-(2,3,4,5,6-pentafluorophenyl) ethylammonium iodide (FEAI), was incorporated into the perovskite solution to act as a passivation layer after formation of the perovskite film. The encapsulated devices show improved stability, maintaining up to 70% of the original PCE after 1000 h at maximum power point (MPP) under constant 1 sun illumination in air. The implementation of the nitrogen-gas flow technique allows the fabrication of PSCs through the slot-die coating process over rigid and flexible substrates using either R2R or batch-to-batch manufacturing and the addition of FEAI additive in the perovskite film increases the stability of the PSCs fabricated using the slot-die coating techniques.