Radiative Annealing of Perovskite Thin Films with Alkyl Halides

Abstract

The performance of the perovskite material in solar cells has garnered a fair amount of interest because it is solution processable and thus a prime target for roll-to-roll coating. The precursor materials are typically prepared in solutions and deposited using common evaporative techniques, some that can be adapted to roll-to-roll manufacturing. The deposited films then must be annealed, a process that is typically accomplished in an oven. The economics of manufacturing improve with increased web speed, which traditional deposition and ovens can handle. However, with a long anneal time the length of the ovens becomes prohibitive, thus processes that can reduce the annealing time are desired. Radiative annealing techniques are often used in the manufacture of solar cells and involve the absorption of intense light energies to induce a thermal response. Our group has been involved in the use of intense pulses of light that can effectively anneal a thin film in under a second. In this work, we report on solution engineering that enables both the deposition of the perovskite in ambient environments using roll-to-roll applicable technologies. The annealing of these thin films is accomplished using 1-5 millisecond flashes of light. The inks formulation includes an alkyl halide that interacts with the light and improving the overall morphology of the perovskite films. Scanning electron microscopy and X-ray diffraction analysis shows that the films achieve consistent morphology and crystallinity and perform well in solar cell devices. Results of several chemistries and processes will be presented.