Perovskite güneş hücreleri için tiyenotiyofen türevli materyallerin sentezi ve özelliklerinin incelenmesi
Synthesis and investigation of thienothiophene based materials for perovskite solar cells applications
Yazar: MELİS ÜNAL
Danışman: PROF. DR. TURAN ÖZTÜRK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı / Kimya Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Kimya = Chemistry

Özet:
Geçmişten günümüze organik materyaller fiziksel ve kimyasal özellikleri sayesinde ilgi odağı olmuştur. Bu ilginin temel sebebi organik moleküllerin kolay modifiye edilebilir olması ve çeşitli modifikasyonlar ile özelliklerinin direkt değiştirilebilmesidir. Organik materyallerin performansları incelendiğinde, elektronik ve optoelektronik çalışma alanlarına uygunluğu anlaşılmış olup son yılların ilgi odağı haline gelmişlerdir. Günümüzde organik ince filmlerin kullanım alanı oldukça genişlemiştir. Bu kullanım alanlarının en başında organik ışık saçan diyotlar (OLED), renkli ekranlar, organik ince film transistörler (OFET), perovskite uygulamaları ve düşük maliyetli etkin güneş pili hücreleri (solar cells (SCs)) gelmektedir.
Optoelektronik malzemeler, foton enerjisi ile elektrik enerjisi arasında tersinir dönüşüm sağlamaktadırlar. Uygun elektron akışını sağlayan donör-akseptör temelli küçük organik moleküllerin dizayn edilmesi ve farklı fonksiyonel gruplar ile modifikasyonu, yüksek performanslı organik materyallerin sentezlenmesini sağlamaktadır. Bu küçük organik moleküller ve iletken polimerler, elektronik ve optoelektronik cihaz yapımının temel taşlarını oluşturmaktadır. Tiyofen temelli organik moleküller çeşitli yöntemler ile fonksiyonlandırılabilmektedirler. Özellikle tiyenotiyofenler (TT) konjuge, kararlı ve iletken yapıları sayesinde organik materyal kimyasında önemli bir yere sahiptir ve bir çok çalışma grubu tarafından incelenmektedirler.
Organik materyaller düşük dielektrik sabitine sahiptir ve bu yüzden elektron-boşluk (hole) etkileşimleri çok yüksektir. İnorganik yarıiletkenler oda sıcaklığında aydınlatma ile serbest elektron ve boşluk üretirler. Organik yarıiletkenler ise soğurma ile zıt kutuplu, yüksek çekime sahip yük çiftleri oluştururlar ve buna "exciton (uyarılmış nükleon)" denir.  Organik güneş pilleri inorganik olanlara kıyasla daha hafif, esnek ve düşük maliyetlidir. Bu sebeple bu pillerin geniş çapta üretimlerinin yapılması amaçlanmaktadır. Organik materyaller, ilk olarak 1954 yılında güneş pili uygulamalarında kullanılmak üzere silikon temelli tasarlanmış ve %6 civarında verim elde edilmiştir. Günümüzde silikon temelli güneş pillerinin verimleri %25 civarında yükseltilmiştir. Bunun yanında diğer organik güneş hücrelerinin verimleri de %15 civarında arttırılmıştır. 
Günümüzde bilinen güneş hücrelerine alternatif olarak perovskite güneş hücreleri üretilmeye başlanmıştır. Adını 1839 yılında Rusya'nın Ural dağlarında keşfedilen bir mineralden almaktadır. Bu mineral, iki farklı katyon tarafından oluşturulan ve her ikisine de bağlanan oksijenler ile çevrelenmiş kristal bir yapıya sahip kimyasal bir bileşimdir. Bu benzersiz kristal yapısı sayesinde elektronların daha uzak ve hızlı geçişine izin veren perovskite güneş hücreleri oda sıcaklığında düşük maliyetler ile üretilebilmeleri, yüksek verimlilik sağlamaları, süperiletkenlik ve elektrik yükünü taşıma kabiliyetleri ile son yıllarda dikkat çekmeye başlamıştır. 
Perovskite güneş hücreleri %20,1 laboratuvar kaydı ile, diğer tüm üçüncü nesil güneş hücrelerinden daha fazla verim sağlamıştır. Geleneksel silisyum güneş hücrelerinden daha ucuz, yüksek verimli bir alternatif güneş hücresi haline gelmiştir. En popüler sentetik perovskite güneş hücresi, metil amonyum kurşun iyodür, yaklaşık %31 teorik maksimum verimliliğe sahiptir [1].
Bu tezin amacı organik materyal kimyası kapsamında perovskite cihaz uygulamalarına yönelik olarak dizayn edilen iletken, tiyenotiyofen temelli malzemelerin sentezi, özelliklerinin (floresans, ultraviyole (UV), döngülü voltametri (CV)) incelenmesi ve cihaz çalışmalarının yapılmasıdır. Analog olarak kullanılan tiyenotiyofen halkaları, donör grup olarak kullanılan yüksek aktiviteye sahip metoksili trifenilamin (TPA(OMe)2) grupları ile birleştirilerek, donör-π-donör (D-π-D) modelli, elektron akışına izin veren moleküller sentezlenecek ve sentezlenen bu materyaller seçinlen alkoksi ve alkil grupları ile fonksiyonlandırılarak değişen özellikleri incelenecektir.
Tüm bu bilgiler doğrultusunda, materyal kimyasına katkı sağlamak amacıyla elektronca zengin, çözünürlüğü yüksek, heterosiklik TT-C6-(TPA(OMe)2)2, TT-PhOMe-(TPA(OMe)2)2 ve TT-Ph-(TPA(OMe)2)3  yapıları elde edilmiştir. Sonuç ürünlere ulaşana kadar elementer bromlama, polifosforik asit ile halka kapama (tiyeno[3,2-b]tiyofen eldesi), NBS ile bromlama ve paladyum katalizörlüğünde Suzuki kenetlenme reaksiyonları gerçekleştirilmiş olup, sentez sonuçları her basamakta 1H-NMR ile ispatlanmıştır.

Abstract:
Organic materials are centre of interest thanks to their physical and chemical properties from past to present. The main reasons of this attention are that this organic molecules can be easily modified, and their modifications directly change their molecule properties. When performances of organic materials are examined, this materials are found suitable for electronic and optoelectronic research interests. Todays, organic thin films are commonly used for various purposes. Especially, organic light emitting diodes (OLED), color displays, organic thin film transistors (OFET), perovskite applications and low cost effective solar cells (SCs) are main study areas.
Optoelectronic materials supply energy conversion between photon and electricity. Designing of small organic molecules which provide suitable electron flow with donor-accepter model, and making modification in their structures with different functional groups enable high performance organic materials to be synthesized. This small organic molecules and conductive polymers are keystones for electronic and optoelectronic devices. Thiophene based organic molecules can be differentiable with various methods. Particularly, thienothiophenes (TT) which have conjugate, stable and conductive structure are highly effective in organic material chemistry, and many researchers examine for them. 
Organic materials have a low dielectric constant and thus their electron-hole interactions are very high. Inorganic semiconductors produce free electrons and holes with lightening at ambient temperature. Organic semiconductors, on the other hand, generate charge-pairs which are named as "exciton". Organic solar cells towards inorganic ones are more weightless, flexible and cost-efficient. Because of these reasons, it is aimed that solar cells are manufactured globally. First of all, in 1954, silicone based organic materials are projected for solar cell applications, and they are obtained with 6% of efficiency. Nowadays, their efficiency is increased about 25% while the others are almost %15. 
In recent years, perovskite solar cells, in addition to common solar cells,  come into use. The peroskite name comes from a mineral which is discovered in Ural mountains in 1839. This mineral is a chemical compound consisting of  two different cations, and the crystal structure is constituted via bonding between oxygen atoms and cations. Perovskite solar cells allow further and faster electron transition thanks to the unique crystal structure. On the other hand, having low cost production at the room temperature, high efficieny, superconductivity and ability of electron transport are most significant properties of perovskite solar cells that attract attention. 
Perovskite solar cells have %20,1 efficiency in the laboratory registration. This yield is higher than all of the other third generation solar cells. These cells become alternative solar cells which are more efficient and cheaper than traditional silicone based ones. The most popular synthetic perovskite solar cell, which is methylammonium lead iodide, has theoretically maximum yield of almost %31 [1].
The aim of this thesis is synthesising of thienothiophene based materials for perovskite solar cell applications within organic material chemistry, analysising of chemical properties with fluorescence, ultraviolet (UV) and cyclic voltammetry (CV), and testing device applications. The thienothiophene rings (TT) are used as analog, and the methoxy triphenylamine groups (TPA(OMe)2) which has high activity are used as the donor. In this study, TT rings will be combined with (TPA(OMe)2) for obtaining donor-π-donor model in same structure. This D-π-D model which allows electron flow will vary with selected alkoxy and alkyl groups, and the modifications of molecule structure will be investigated.
In the light of this information, TT-Ph-OMe-(TPA(OMe)2)2, TT-C6-(TPA(OMe)2)2 and TT-Ph-(TPA(OMe)2)3 molecules have been synthesized in order to contribute organic material chemistry, and 1H-NMR technique has been used to establish. It has been observed that these heterocyclic molecules have high solubility and electron density.
	Synthesis of 1-(thiophen-3-ylthio)octan-2-one (2) : 3.0 g (18.4 mmole) of 3-bromothiophene was dissolved in 50 mL dry diethyl ether. 13.8 mL (1.2 equivalent) of n-buthyllithiım (1.6 M) was added dropwise at -78°C under nitrogen atmosphere. After 40 minutes for stirring, 0.62 g (1.05 equivalent, 19.32 mmole) of elemental sulfur was added and stirred for 40 minutes. 4.6 g (1.2 equivalent, 22.21 mmole) of 1-bromooctan-2-one was added into the mixture, and after 1 hour, the machine was turned off. The mixture was stirred for nightlong, and the solution was extracted with sodium carbonate and water. The organic phase was dried with sodium sulphate and filtered. The mixture was purified with column chromatography (4hexane:1DCM). The product (2.45 g) was obtained with %55 yield.
	Synthesis of 1-(4-methoxyphenyl)-2-(thiophen-3-ylthio)ethanone (3) : 2.0 g (12.27 mmole) of 3-bromothiophene was dissolved in 40 mL dry diethyl ether. 9.20 mL (1.2 equivalent) of n-buthyllithiım (1.6 M) was added dropwise at -78°C under nitrogen atmosphere. After 45 minutes for stirring, 0.41 g (1.05 equivalent, 12.88 mmole) of elemental sulfur was added and stirred for 45 minutes. 3.37 g (1.2 equivalent, 14.72 mmole) of 2-bromo-1-(4-methoxyphenyl)ethanone was added into the mixture, and after 1 hour, the machine was turned off. The mixture was stirred for nightlong, and the solution was extracted with sodium carbonate and water. The organic phase was dried with sodium sulphate and filtered. The mixture was purified with column chromatography (7hexane:1DCM). The product (2.92 g) was obtained with %90 yield.
	Synthesis of 1-(4-bromophenyl)-2-(thiophen-3-ylthio)ethanone (4) : 2.0 g (12.27 mmole) of 3-bromothiophene was dissolved in 40 mL dry diethyl ether. 9.20 mL (1.2 equivalent) of n-buthyllithiım (1.6 M) was added dropwise at -78°C under nitrogen atmosphere. After 45 minutes for stirring, 0.41 g (1.05 equivalent, 12.88 mmole) of elemental sulfur was added and stirred for 45 minutes. 4.09 g (1.2 equivalent, 14.72 mmole) of 2-bromo-1-(4-bromophenyl)ethanone was added into the mixture, and after 1 hour, the machine was turned off. The mixture was stirred for all night, and the solution was extracted with sodium carbonate solution. The organic phase was dried with sodium sulphate and filtered. The mixture was purified with column chromatography (6hexane:1DCM). The product (3.08 g) was obtained with %85 yield.
	Synthesis of 3-hexylthieno[3,2-b]thiophene (5) : 4.04 g (10 equivalent, 41.26 mmole) of polyphosphoric acid (PPA) and 5 mL of chlorobenzene was putted into three-necked glass flask, and stirred at 135°C until dissolving of PPA. After 1.0 g (4.12 mmole) of molecule (2) in 5 mL of chlorobenzene was heated into another flask at 70°C, it was added drop by drop onto PPA. The mixture was stirred for 5 hours. Organic phase was taken into fume cupboard to volatilize chlorobenzene, and PPA phase was extracted with sodium carbonate and water. The product was purified with column chromatography (5hexane:1DCM) and obtained (0.81 g) with %87 yield.
	Synthesis of 3-(4-methoxyphenyl)thieno[3,2-b]thiophene (6) : 3.71 g (10 equivalent, 37.83 mmole) of polyphosphoric acid (PPA) and 5 mL of chlorobenzene was putted into three-necked glass flask, and stirred at 135°C until dissolving of PPA. After 1.0 g (3.78 mmole) of molecule (3) in 5 mL of chlorobenzene was heated into another flask at 70°C, it was added drop by drop onto PPA. The mixture was stirred for 5 hours. Organic phase was taken into fume cupboard to volatilize chlorobenzene, and PPA phase was extracted with sodium carbonate solution. The product was purified with column chromatography (6hexane:1DCM) and obtained (0.79 g) with %85 yield.
	Synthesis of 3-(4-bromophenyl)thieno[3,2-b]thiophene (7) : 3.13 g (10 equivalent, 31.92 mmole) of polyphosphoric acid (PPA) and 5 mL of chlorobenzene was putted into three-necked glass flask, and stirred at 135°C until dissolving of PPA. After 1.0 g (3.19 mmole) of molecule (4) in 5 mL of chlorobenzene was heated into another flask at 70°C, it was added drop by drop onto PPA. The mixture was stirred for 5 hours. Organic phase was taken into fume cupboard to volatilize chlorobenzene, and PPA phase was extracted with sodium carbonate and water. The product was purified with column chromatography (8hexane:1DCM) and obtained (0.75 g) with %80 yield.
	Synthesis of 2,5-dibromo-3-hexylthieno[3,2-b]thiophene (8) : 0.32 g (1.43 mmole) of molecule (5) was dissolved in 7 mL of N,N-dimethylformamide and waited in ice-bath for 15 minutes. 0.558 g (2.2 equivalent, 3.14 mmole) of N-bromosuccinimide was added into the mixture in dark, and the mixture was stirred into ice-bath for 12 hours without light. The mixture was poured with water and waited in refrigeratore for 15 minutes to precipitate. After extraction with sodium bicarbonate and water, the mixture was dried with sodium sulphate and filtered. The product (0.46 g) was obtained with %85 yield.
	Synthesis of 2,5-dibromo-3-(4-methoxyphenyl)thieno[3,2-b]thiophene (9) : 0.5 g (2.03 mmole) of molecule (6) was dissolved in 6 mL of N,N-dimethylformamide and waited in ice-bath for 15 minutes. 0.79 g (2.2 equivalent, 4.47 mmole) of N-bromosuccinimide was added into the mixture in dark, and the mixture was stirred into ice-bath for 12 hours without light. The mixture was poured with water and waited in refrigeratore for 15 minutes to precipitate. After extraction with sodium bicarbonate and water, the mixture was dried with sodium sulphate and filtered. The product (0.66 g) was obtained with %80 yield.
	Synthesis of 2,5-dibromo-3-(4-bromophenyl)thieno[3,2-b]thiophene (10) : 0.5 g (1.69 mmole) of molecule (7) was dissolved in 5 mL of N,N-dimethylformamide and waited in ice-bath for 15 minutes. 0.66 g (2.2 equivalent, 3.73 mmole) of N-bromosuccinimide was added into the mixture in dark, and the mixture was stirred into ice-bath for 12 hours without light. The mixture was poured with water and waited in refrigeratore for 20 minutes to precipitate. After extraction with sodium bicarbonate solution, the mixture was dried with sodium sulphate and filtered. The product (0.69 g) was obtained with %90 yield.
	Synthesis of 4,4'-(3-hexylthieno[3,2-b]thiophene-2,5-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (13) : 0.2 g (0.52 mmole) of molecule (8) and 0.5 g (2.2 equivalent, 1.16 mmole) of B-TPA(OMe)2 were dissolved in 40 mL of THF. 3 g of potassium carbonate with 10 mL distilled water was added into the reaction reactor under nitrogen atmosphere. Pd(0) was added as catalyst, and the mixture was stirred in reactor under nitrogen atmosphere for 5 minutes. Then, reactor was heated to 80°C for 2 days. For removing Pd(0), the mixture was leached out of celite with DCM. After THF was volatilized, the mixture was extracted with brine, dried with sodium sulphate and filtered. After column chromatography with hexane, the product was precipitated with cold methanol and waited in drying oven. The pure product (0.24 g) was obtained with %55 yield.
	Synthesis of 4,4'-(3-(4-methoxyphenyl)thieno[3,2-b]thiophene-2,5-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (14) : 0.2 g (0.49 mmole) of molecule (9) and 0.47 g (2.2 equivalent, 1.09 mmole) of B-TPA(OMe)2 were dissolved in 40 mL of THF. 3.0 g of potassium carbonate with 10 mL distilled water was added into the reaction reactor under nitrogen atmosphere. Pd(0) was added as catalyst, and the mixture was stirred in reactor under nitrogen atmosphere for 5 minutes. Then, reactor was heated to 80°C for 2 days. For removing Pd(0), the mixture was leached out of celite with DCM. After THF was volatilized, the mixture was extracted with brine, dried with sodium sulphate and filtered. After column chromatography with 10hexane:1DCM, the product was precipitated with cold methanol and waited in drying oven. The pure product (0.25 g) was obtained with %60 yield.
	Synthesis of 4,4'-(3-(4'-(bis(4-metoksifenil)amino)-[1,1'-bifenil]-4-il)tiyeno[3,2-b]tiyofen-2,5-diil)bis(N,N-bis(4-metoksifenil)anilin) (15) : 0.2 g (0.44 mmole) of molecule (10) and 0.63 g (3.3 equivalent, 1.46 mmole) of B-TPA(OMe)2 were dissolved in 55 mL of THF. 3.0 g of potassium carbonate with 10 mL distilled water was added into the reaction reactor under nitrogen atmosphere. Pd(0) was added as catalyst, and the mixture was stirred in reactor under nitrogen atmosphere for 5 minutes. Then, reactor was heated to 80°C for 2 days. For removing Pd(0), the mixture was leached out of celite with DCM. After THF was volatilized, the mixture was extracted with brine, dried with sodium sulphate and filtered. After column chromatography with 8hexane:1DCM, the product was precipitated with cold methanol and waited in drying oven. The pure product (0.32 g) was obtained with %65 yield.