A Series of Novel Silicon Phthalocyanines/ Naphthalocyanine as Near Infrared Sensitizers in Organic Ternary and Quaternary Solar Cells

Language
en
Document Type
Doctoral Thesis
Issue Date
2017-02-06
Issue Year
2017
Authors
Ke, Lili
Editor
Abstract

Bulk heterojunction (BHJ) solar cells based on polymer/fullerene blends have attracted much attention over the last decade, leading to a breakthrough in power conversion efficiency (PCE) over 10%. Several strategies are currently being pursued to achieve higher PCE, while most conjugated polymers have an intense, but rather narrow absorption band. An attractive method to broaden the absorption bandwidth is to blend near infrared (near IR) sensitizers into the host donor:acceptor binary blend system. Among them, dye molecules are the most widely used. This dissertation targets on the synthesis of novel dye molecules and fabricating of high efficiency ternary solar cells with absorption ranges extending into the near IR region. The first part of this thesis focuses on design and synthesis of silicon phthalocyanines (SiPCs) and naphthalocyanine (SiNC) to open the possibility to modify the chemical, electronic and optical properties. Hence, a novel series of SiPCs (SiPC-0, SiPC-1, SiPC-2, and SiPC-3) with varying the length of alkyl chain between the pyrene ring and PC ring, and SiNC-1 by extending the π-system structure were synthesized according to a simple method and characterized. The electronic and optical properties of all new compounds were investigated separately by using cyclic voltammetry and UV-vis absorption spectroscopy methods. Near IR absorption feature and suitable band gap (Egap) give these molecules great potential to implement them in ternary or quaternary organic solar cells as dye sensitizers. The second part of this thesis focuses on study of the relationship between materials’ structure with their physical properties and with device application. Introducing SiPC compounds into P3HT/PCBM matrix, all sensitizers showed a strong photosensitivity in the near IR region and notable improvement for all performance parameters of the ternary solar cells as compared to the reference binary device. The incorporation of SiPC-3 resulted in an increase of up to 21.9% of short-circuit current density (JSC), 16.1% of open-circuit voltage (VOC) and 7.2% of fill factor (FF), leading to an improvement of up to 51.6% of PCE in ternary solar cells. Charge generation, transport properties and morphology of the ternary systems were studied by using different advanced technologies to exhibit the relationship between the molecule structures with photophysical properties. The third part of this thesis focuses on the study of ternary and quaternary concept and on the revealing the charge transfer/transport mechanism. Herein, we studied the application of SiNC-1 as an efficient photosensitizer in ternary solar cells as well as in quaternary ones, incorporating SiPCs as the complementary near IR sensitizers to the SiNC-1. Our in-depth study based on the optoelectronic internal quantum efficiency (IQE), photoluminescence (PL) and photoinduced absorption (PIA) measurements revealed complex charge transfer and transport kinetic in ternary systems. Multi-colored dye sensitized device covering the UV-vis as well as near IR regions from 350 up to 900 nm outlined apparent signal characteristics of each single dye. It corroborated the effective contribution of both SiPC and SiNC dyes in enhancing the JSC and device performance. And finally, the last part of this thesis focuses on high efficiency ternary solar cells based on middle band gap polymer host systems and on VOC change implementing different content of SiPC sensitizer. Herein, the best silicon phthalocyanine SiPC-3 was introduced into OPV-46:PCBM and PCDTBT:PCBM host systems as the near IR sensitizer. Different to the crystalline polymer systems, amorphous ones allow more dye loading with stronger near IR photosensitivity, yielding an improvement of JSC. Interestingly, different VOC trend were observed for these two amorphous polymer systems.

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