Intense Pulse Light Annealing of Perovskite Photovoltaics Using Gradient Flashes

Abstract

Perovskite solar cells (PSCs) have been fabricated through high-speed and low-cost depositions but often require long annealing. Intense pulse light (IPL) can anneal thin films in seconds after deposition by inducing very high temperatures lasting for milliseconds, and multiple flashes can be used to tune the temperature profile. In this study, a gradient flash annealing (GFA) approach is introduced and compared to uniform flash annealing (UFA) by investigating the crystallinity, morphology, and phase evolution of the CH3NH3PbI3 perovskite films and their impact on PSC performance. Unlike UFA, low-intensity pulsed irradiation during the pre-annealing stage of GFA played a significant role on enhancing the PSC performance by forming pure-phase CH3NH3PbI3 perovskite thin films with superior morphology and high crystallinity. To understand the kinetics, a transient thermal simulation using ANSYS was developed and confirmed with an experimental setup. The results combined with microscopy and spectrophotometry were used to visualize how duration, delay time, photon flux, and flash count parameters participated in crystallization, phase, and morphology evolution. The IPL annealing induced rapid surface temperature increase, reaching as high as 800 °C, while produced well-developed and bound perovskite grains without any surface defects in an uncontrolled ambient environment with high humidity (>60%). The study resulted in PSCs with maximum efficiency and fill factor of 9.27 and 69.92% for the UFA and 11.75 and 68% when annealed through the GFA approach, respectively. This work utilized IPL as the sole thermal source for post-deposition annealing to rapidly fabricate efficient PSCs in only 10 s, which opens the pathway for high-speed, low-cost, and large-scale automated fabrication of perovskite photovoltaics and semiconductors.

Automated Fabrication of Perovskite Photovoltaics Using Inkjet Printing and Intense Pulse Light Annealing

“…As previously reported, IPL releases intense flashes carrying energetic photons once absorbed by the material, converts into phonons that aid in crystallizing the material, and enables charge transport. [43,45,48] The intensity of the PL peak is considerably higher for the perovskite films deposited on FTOglass than on IPL annealed SnO 2 films, indicating charge transfer at the perovskite/SnO 2 interface upon annealing. X-ray diffraction (XRD) patterns showing the phase purity of the processed perovskite are shown in Figure 5B, where the film is processed as stated in a previous work.…”

“…X-ray diffraction (XRD) patterns showing the phase purity of the processed perovskite are shown in Figure 5B, where the film is processed as stated in a previous work. [48] The intense 2θ peaks around 14.1 , 20 , 23. The XRD pattern revealed no PbI 2 peaks at 12.4 , [49,50] indicating fabrication of pure perovskite black phase and evaporation of water content during IPL annealing of SnO 2 .…”

“…Upon printing, the slides were transferred to the IPL annealing station (Sinteron S-2210, Xenon Corp.) where they were successfully annealed similar to our previous report [45] by exposing five flashes, each with the duration, energy, and interval time between flashes of 2 ms, 2.1 kJ (9 J cm À2 ), and 1 s, respectively. Upon SnO 2 fabrication, the CH 3 NH 3 PbI 3 perovskite film was spin coated and directly annealed through IPL, similar to our previous work, [48] but with a slight modification to the precursor chemistry. In brief, 0.6454, 0.2226, and 0.023 gr of PbI 2 , MAI, and MACl were initially dissolved in 1 mL dimethylformamide (DMF), 0.125 mL dimethyl sulfoxide (DMSO), and 20 μL N-methyl-2-pyrrolidone (NMP), followed by adding 0.25 mL di-iodomethane and stirring for 2 h. Upon annealing, the electrode places covered with perovskite were wiped off using cotton swabs dipped in gamma butyrolactone (GBL).…”

“…This annealing method has been exhaustively studied on various PSC thin films, particularly the TiO 2 and SnO 2 ETL, [44][45][46] as well as perovskite films. [37,38,45,47] Recently, our group introduced the rapid fabrication of PSCs, where the ETL and perovskite films were directly annealed through IPL in a total of 10 s, [48] indicating the promising role of this method toward rapid scalable fabrication of PSCs. However, like other works, the fabricated PSCs utilized thermally evaporated metal back contacts, which is a hindrance for automation.…”

Annealing Engineering in the Growth of Perovskite Grains

“…The intense pulsed light is a non-contact rapid heating method which can offer fast millisecond pulses of broad spectrum light (190-1100 nm) from xenon lamps [74]. Xenon lamps are used to provide high-energy pulse light to 150 J/cm 2 for perovskite annealing, and can achieve thin film crystallization at the millisecond scale [54,70,[75][76][77][78][79]. Druffel et al successfully employed intense pulsed light generated by a xenon lamp to sintering of MAPbI 3 on a mesoporous TiO 2 substrate for first time [76].…”