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Study on the Preparation, Characterization of BiOI/Bi₂S₃and Bi₂S₃/P3HT Heterojunction Films and on Their Photoelectric Conversion Properties

Author: FangMingQing
Tutor: ZhangLiZhi;ZhengZhi
School: Central China Normal University
Course: Physical and chemical
Keywords: BiOI/Bi2S3 Bi2S3/P3HT Photoelectrochemical Heterostructures Inorganic-Organic Hybrid Solar Cells
CLC: TQ135.32
Type: Master's thesis
Year: 2014
Downloads: 1
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Abstract

BiOI is a p-type semiconductor with suitable bandgap, low cost and environment friendly properties, which has been applied widely in photocatalysis, electrochemical hydrogen storage and photoelectrochemical solar cells. The energy conversion efficiencies of BiOI based photoelectrochemical solar cells reported before were low, one main reason was that electron-hole pairs produced by BiOI after illumination separated inefficiently. In order to improve the energy conversion efficiency, we combined BiOI with Bi2S3to form heterostructures at room temperature through a facile and economical ion exchange method. The heterostructure films were characterized by XRD, SEM, TEM, XPS, Raman, UV-vis and SPV. Results indicated that Bi2S3and BiOI in the films were amorphous and crystalline, respectively. The optical absorption of heterostructure films were broadened and enhanced. I-V and IPCE measurements showed that the energy conversion efficiency of heterostructure film, with appropriate reaction time, based photoelectrochemical solar cell was much higher than the energy conversion efficiency of BiOI based cell. The detailed photovoltaic performance parameters of the best cell are Jsc=0.65mAcm"2, Voc=0.50V, FF=0.40and η=0.36%. We attribute the better performance mainly to the efficiently charge separate and secondary to the improvement of light absorption after BiOI/Bi2S3heterojunction formed.Liquid state solar cells are suffering from electrolyte leakage and corrosion of the counter electrode. The research enthusiasm of the photovoltaic scientists concentrates on all solid state solar cells, especially the inorganic-organic hybrid solar cells which combine the advantages including the flexibility, light weight, and low fabrication costs of polymer materials and the high electron mobility, size-dependent optical properties, and physical and chemical stability of inorganic nanocrystals. Herein, we report on inorganic-organic hybrid solar cells based on Bi2S3/P3HT active layer, where the P3HT layer serves as the electron donor and transports photogenerated holes, whereas the Bi2S3accepts and transports electrons. Energy level positions of Bi2S3and P3HT are beneficial to the separation and transportation of charge carriers. Bi2S3nanospheres with diameter between20to50nm were fabricated by alternate solution immersion method at a low temperature. After optimizing the growth number, we obtained the best device with Jsc of 0.405mAcm-2, Voc of0.155V, FF of0.29and ηof0.0183%. Moreover, we found that the addition of2wt%graphene of high carrier mobility and conductivity into the P3HT solution can improve the conductivity of polymer film and thus enhance the photovoltaic performance of solar cell from0.017%to0.049%.There are three innovative points in this thesis:1) The preparation for BiOI/Bi2S3and Bi2S3/P3HT heterostructures was all performed at a low temperature, requiring low energy consumption. Aqueous solution was used as reaction system. No surfactants and poisonous, harmful, expensive reagents were needed. The result films are uniform, innocuous, unpoisonous, and environmental friendly, and can be manufactured in short period and large-scale.2) Bi2S3nanospheres were grown in-situ on BiOI nanoflake films, uniformly. Abundant BiOI/Bi2S3heterojunction were formed, which can improve the light absorption efficiency and carrier separation efficiency, resulting in better photoelectric conversion efficiency of the devices. The in-situ growth method can avoid a series of of problem, such as aggregation of particles, microstructure destruction, impurities introduction, high temperature annealing, and bad mechanical stability.3) ITO/PET flexible substrates were applied for BiOI/Bi2S3devices, which is appealing for low-cost, large-area, roll-to-roll application as in the manufacturing of third generation thin-film photovoltaics.

Study on the Preparation, Characterization of BiOI/Bi2S3and Bi2S3/P3HT Heterojunction Films and on Their Photoelectric Conversion Properties

Abstract

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Study on the Preparation, Characterization of BiOI/Bi₂S₃and Bi₂S₃/P3HT Heterojunction Films and on Their Photoelectric Conversion Properties