High Performance Perovskite Photodetectors
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Organohalide lead perovskite (CH3NH3PbI3) is a novel material with promising applicability for visible light photo-detectors. The ability to develop perovskite photodetector devices using a low temperature solution based process allows straightforward combinations with other materials, including traditional crystalline semiconductors, with minimal contributions to cost and process complexity. Lab-scale perovskite photodetectors and solar cells grown using traditional single, or multiple, precursor deposition steps are typically plagued by low film uniformity and reproducibility. This not only limits optimal device performance, but also provides for highly variable results. In traditional two-step processing, a film of layered lead iodide (PbI2) is grown, followed by application of methyl-ammonium iodide (MAI). These precursor compounds react uncontrollably before MAI can fully intercalate into the spaces separating the layers of PbI2. This work presents a novel two-step perovskite growth technique which utilizes methyl-ammonium acetate (MAAc) to better control precursor reaction/perovskite crystallization, yielding thin films which have improved uniformity and reproducibility. Perovskite films grown using our novel two-step processing, as well as traditional growth techniques, are characterized using various metrology techniques. Additionally, devices fabricated with, and without, MAAc undergo current-voltage characterization under AM1.5G simulated solar light, as well as external quantum efficiency measurements. In addition to the need for more uniform and reproducible perovskite films, there is a need for high-resolution structuring of these xiii films to minimize cross-talk between neighboring detectors (pixels) for imaging purposes. This work presents a method to develop CH3NH3PbI3 thin films possessing high-resolution patterning, using lithography processing with hydrofluoroether solvents. The results presented herein confirm that, unlike the majority of traditional solvents utilized in conventional photolithography, hydrofluoroethers do not adversely affect CH3NH3PbI3 films, enabling photolithographic processing. Transfer of the resist pattern is achieved using a SF6 plasma functionalization process which extracts iodine and organic components from the film, converting the perovskite into PbF2. This work also demonstrates that isolation of perovskite photodetecting pixels with a 20 µm-wide stripe of PbF2 leads to a 4.5-fold reduction in the cross-talk between neighboring pixels. It is believed that our method will facilitate simple monolithic integration of perovskite photodiodes to the silicon backplane chip utilized in active-pixel sensor and charge-coupled device applications.