Inexpensive fluorene-based hole transporting material with terminated thiophene unit for efficient semi-transparent Sb2S3 solar cells
Aistė Jegorovė a, Sreekanth Mandati b, Nimish Juneja b, Atanas Katerski b, Aivars Vembris c, Raitis Grzibovskis c, Vytautas Getautis a, Tatjana Dedova b, Artiom Magomedov a, Nicolae Spalatu b, Smagul Karazhanov d, Malle Krunks b, Ilona Oja Acik b
a Department of Organic Chemistry, Kaunas University of Technology, Kaunas LT-50254, Lithuania.
b Laboratory of Thin Film Chemical Technologies, Department of Materials and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.
c Institute of Solid State Physics, University of Latvia, Kengaraga Str. 8, Riga, Latvia.
d Institute for Energy Technology (IFE), P.O Box 40, NO 2027, Kjeller, Norway.
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Aistė Jegorovė, 226
Publication date: 20th April 2022

The Sun is known to be the most powerful source of energy. Solar cells are devices that convert absorbed light into electricity and silicon solar cells are currently the most commonly used technology to do that. However, it has its own drawbacks and other high efficiency solar cell technologies have been developed. Solid-state semiconductor-sensitized solar cells (antimony sulphide solar cells (Sb2S3 SCs)) have recently emerged as a promising technology for the further cost reduction of the energy production from the sunlight. Although Sb2S3 SCs does not outperform silicon solar cells it has its own advantages, for example simple Sb2S3 layer deposition methods, thermal stability and humidity resistance of absorber, etc. [1, 2, 3] However, there are several obstacles that need to be addressed for it to see a widespread use. One of them is the use of expensive charge-transporting semiconductors such as Spiro-OMeTAD, PCPDTBT, etc. [4, 5]. P3HT is also often used as HTM in Sb2S3 SCs. However it has parasitic absorption in visible spectral region [6]. Therefore, there is a vigorous search for cheaper and simpler methods for the synthesis of organic semiconductors. According to the literature fluorene chromophores are among the most popular structural building blocks, used for other emerging technologies as organic hole-transporting materials (HTMs)  [7‒9. Furthermore thiophene-based compounds are widely used as HTM’s in Sb2S3 SCs [5, 10, 11].

In this work we synthesized fluorene-based compound, containing methoxyphenyl- and thiophene chromophores, that have been obtained by a simple synthetic method. Thermal and photoelectrical properties were investigated, and photovoltaic device was constructed.

The new hole transporting material (V808) was realized under Hartwig-Buchwald amination conditions using commercially available starting materials. New compound bear fluorene fragment with thiophene substituent in 9H position as molecule-core, while 4,4’-dimethoxydiphenylamine was used to build side chromophores. New HTM exhibit good thermal stability, at up to 390 °C. Nevertheless, compound has an amorphous state, which is important for homogenous films forming. The ionization potential (Ip) of target material is  4.95 eV which is suitable for using this compound as HTM in Sb2S3 solar cells. The PCE of the most efficient n-i-p Sb2S3 device possesing V808 have reached 3.8 % (3.6 % for P3HT). Furthermore, new structure show good transparency, which is higher than P3HT.

The “Development of Semi‐Transparent Bifacial Thin Film Solar Cells for Innovative Applications” benefits from a 999372 € grant from Iceland, Liechtenstein and Norway through the EEA Grants. The aim of the project is to develop new approach based on novel materials and structures and production technologies, which are the key to further increase the share, and range of application of PV in areas with sub‐average sunlight, including Baltic and Nordic countries. Therefore, development of resource saving, cost‐effec􀆟ve and efficient PV devices is a primary challenge of this project.  

Project contract with the Research Council of Lithuania (LMTLT) No is S-BMT-21-1(LT08-2-LMT-K-01-003).  

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