Venkatesan Govindan

• Main Authors: Govindan, Venkatesan
• Other Authors: Chun-Guey Wu
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/3979sn

博士 === 國立中央大學 === 化學學系 === 107 === Abstract This thesis is the work on the organic semiconductors for applications as electron donor (p-type) materials in organic solar cells (OSCs), hole transporting materials (HTMs) in inverted perovskite solar cells (p-i-n PSCs) and electron transporting materials (ETMs) in regular perovskite solar cells (n-i-p PSCs). The synthesis and physicochemical characterization of new materials (P-type, HTMs and ETMs) were reported. The structure-property relationship and the photovoltaic performance of the corresponding cells were investigated. The first part focuses on synthesis of four donor–donor–acceptor–donor– donor (D1–D2–A–D2–D1) type small molecules (SM1, SM2, SM3 and SM4), in which diketopyrrolopyrrole (DPP) was used as an acceptor (DPP) core and 3,4-ethylenedioxythiophene (EDOT), triphenylamine (TPA) or alkyl thiophene (AT) acted as a donor using direct arylation reaction. The inverted small molecule solar cell (using PCBM as an acceptor, and ZnO and MoO3 as the electron and hole transporters, respectively) based on SM2 has the highest value of Voc (0.82 V) due to SM2 having the lowest HOMO level. Two acceptor– donor–acceptor type (A–D–A) molecules (SM5 and SM6) were also synthesized by Stille coupling, in which DPP and EDOT were used as the acceptor and donor, respectively. SM5 and SM6 are structural isomers, however the inverted cell based on SM6 has a much higher PCE than that based on SM5, due to SM6 having better solubility and a lower HOMO energy level. The second part targets on four heterocyclic spiro-typed hole transporting materials (HTMs) carrying spiro[fluorene-9,9’-xanthene] (SFX) such as SFXTPAM and SFX-TPA or spiro[fluorene-9,9’-thioxanthene] (SFT) unit such as SFT-TPAM and SFT-TPA were synthesized through low cost facile route with high yields. The photovoltaic performance of the inverted PSCs based on these small molecular hole transporting materials with the device architecture of glass/ITO/HTM/CH3NH3PbI3/C60/BCP/Ag was studied. Inverted PSC based on dopant-free SFX-TPAM HTM achieves a power conversion efficiency of10.23% under the illumination of standard one Sun lighting, which is better than that (8.17%) of the cell based on dopant-free spiro-OMeTAD. The third part is the preparation and photovoltaic application of three fullerene based ETMs (C60-RT2, C60-RT6 and C70-RT2), in which fullerene (C60 and C70) as core unit and bis(2-(2-((tert-butoxycarbonyl)amino)ethoxy)ethyl) malonate (4b) was used as a substituent. All three fullerene exhibit very good solubility in polar protic solvents (such as methanol, ethanol and water), which is beneficial for making of low temperature processed ETMs for regular PSCs. The new fullerene derivatives were mixed with low temperature processed TiO2 to be used as ETMs in regular PSCs (FTO/ETMs/PSK/Spiro- OMeTAD/MoO3/Ag). Cells based on new ETMs have the PCE of 16.37% (TiO2+C60-RT2), 18.03% (TiO2+C60-RT6) and 17.10% (TiO2+C60-RT6), which is higher than that (14.92%) of the cell based on TiO2 ETL. The work of this thesis provides valuable guideline for designing charge transporting materials for photovoltaic application.