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|Title:||Highly Efficient and Stable Inverted Perovskite Solar Cells with Inorganic Charge Transport Layers|
|Publisher:||Quaid-i-Azam University, Islamabad.|
|Abstract:||The fabrication and characterization of inverted perovskite solar cells (PSCs) with inorganic materials for charge transport is presented in this dissertation. Hybrid organic inorganic perovskites (HOIP) materials are considered promising for the solar cell applications for their novel properties, high absorption coefficient, ambipolar chargecarrier mobilities, long exciton lifetimes and diffusion lengths, and low exciton binding energy. Although, perovskite solar cells (PSCs) have achieved a very high power conversion efficiency but long-term stability, current hysteresis and lead-toxicity are the major concerns in its commercialization. Different techniques have been employed to overcome these issues. Use of inorganic charge transport layer have demonstrated relatively stable PSCs. With this motivation, we have synthesized PSCs with zinc selenide for electron transport and nickel oxide (NiOx) for hole transport. Zinc Selenide (ZnSe), before applying in perovskite solar cells, are deposited by simple thermal evaporation with different thicknesses. Post-deposition annealed assisted crystalline phase refinement is studied. The composition analyses carried out by the Rutherford backscattering spectroscopy have shown the ratios of Zn: Se to be 1:1. The crystallinity of the ZnSe samples improves with annealing temperature, hence, increase of conductivity and optical bandgap of the samples. The population of the localized trapping centers near the valence band top edge of ZnSe diminishes significantly with the postannealing that refines the band gap; optimizes their electrical and optical properties. Chapter 4 describes the synthesis of formadinium lead iodide (FAPbI3) films deposited by spin coating techniques and annealed at various temperature for investigation of perovskite phase formation temperature and check its effect on morphology and optical properties. By using these materials, inverted perovskite solar cells devices were studied. Devices with FAPbI3 annealed at 130oC and higher temperature have shown power conversion efficiency ~11 %. Secondly, methylammonium formamidinium lead iodide bromide (FAPbI3)1-x (MAPbBr3)x (x= 0, 0.05, 0.1, 0.15, 0.2 and 1) were used as absorbing layer in PSCs with best efficiency of 14.99% is observed with x=0.1. A conjugated organic molecule, bathocuproine (BCP), is often deposited on C60 for the electron collection of inverted perovskite solar cells (PSCs). But organic molecules are not stable against UV light and cannot protect the perovskite layer. In principle, inorganic - x - materials can have better stability. But the thermal deposition of inorganic materials usually requires very high temperature. In chapter 5, zinc selenide (ZnSe), a two-dimensional (2D) II-VI semiconductor material having wide bandgap and high electron mobility, is investigated for the electron collection of PSCs without BCP. The ZnSe layer is deposited by using a normal thermal evaporator. The PSCs with ZnSe can exhibit a power conversion efficiency (PCE) of 18.38%, comparable to the PSC with BCP. Use of inorganic charge transport layer have demonstrated relatively PSCs. Among inorganic materials for hole transport, NiOx is one of the most widely used HTL in inverted PSCs and different techniques and doping in this layer have been reported so far in order to improve the performance of these devices. Chapter 6 describes the synthesis of NiOx thin film which act as hole transport layer on glass substrate at the initial stage and PSC devices were fabricated at the secondary stage. Post deposition annealing temperature effects the composition and tuning of the work function and aligning it with perovskite work function to increase the hole transport efficiency and improves Voc of devices from 0.96V to 1.08V. Devices with NiOx as HTL and ZnSe as ETL are also studied and performance of devices is also included. In addition, the comparative stability results of the devices are also included.|
|Appears in Collections:||PhD Thesis of All Public / Private Sector Universities / DAIs.|
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|Muhammad Imran_Phy_2020_QAU_PRR.pdf||phd.Thesis||7.18 MB||Adobe PDF||View/Open|
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