Hole Transport Layer optimization for Methylammonium Lead Iodide Photovoltaic Cell
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The innovation of hybrid halide perovskite solar cells has gained a noticeable advancement in the domain of photovoltaics. Despite of this upsurge in performance and its low cost, the materials that constitute a solar cell have different stability issues which hinder its performance and its commercialization. The hole transport layer is considered one of the most important material in perovskite solar cells. It plays a role in performance optimization, reducing recombination of charge carriers and aligning energy level with the contact layers. Besides hole transport layer, the perovskite methylammonium lead iodide itself is known be unstable at different temperatures, and, as a result, the device suffers from degradation. Temperature stability has also been associated with the phase change of the perovskite crystal structure. Moreover, the ions that constitute the perovskite layer are also known to be mobile which can have positive or negative effects to device performance. This work will investigate an organic polymer Poly[bis(4- phenyl)(2,4,6-trimethylphenyl)amine as a hole transport layer in methylammonium lead iodide perovskite solar cell. The devices made with this hole transport layer should enhance the device performance and even maintain its easy fabrication methods. The hole transport layer was first characterized for its physical and electrical properties after which the performance of the photovoltaic device was measured under standard AM1.5G solar illumination. The performance parameters were obtained by fitting the current-voltage curve employing a two-diode model. Device performance was also tested at different temperatures, which showed the phase transition of perovskite from orthorhombic to tetragonal to cubic in the temperature range less than 165 K to 165 K to 327 K to temperature greater than 327 K respectively. Stability tests with light soaking and electrical biasing revealed that the degradation in device performance is indeed reversible due to ion-migration.