Join our seminar on 25 April

Time: 17:00 – 18:00

Place: TPOC-3, Nobel str., Blue Building, Room 402

Speaker: Irina Klimovich, Center for Electrochemical Energy Storage

Title: Design of conjugated polymers for organic solar cells

Abstract: Organic solar cells have attracted much attention for few decades because of their easy processing, low cost, light-weight, flexibility and possibility of fine tuning of electronic properties of photoactive materials. My talk will be divided in two parts and dedicated to push-pull donor-acceptor conjugated polymers for conventional polymer-fullerene solar cells as well as block copolymers for devices with single material photoactive layer.

Great improvement in the performance of organic bulk-heterojunction solar cells was achieved mostly due to successful design of novel photoactive materials. Recently, promising electron-donor copolymers (X-TTBTBTT-)n (X – fluorine, carbazole; B –benzothiadiazole; T – thiophene) have been developed, which demonstrate good performances both in spin-coated (up to 7%) and roll-to-roll processed (up to 6.2%) devices.

In the present work we were aiming to improve further the optoelectronic characteristics of the designed copolymers (X-TTATATT-)n via a systematic variation of the acceptor (A) units. We synthesized and investigated materials based on 2-alkylbenzotriazole, several different quinoxaline derivatives, benzoxadiazole and 5,6-bis(octyloxy)benzoxadiazole. We will discuss how the chemical structure of the acceptor building blocks affects the optoelectronic and physicochemical properties of the materials as well as their performance in organic solar cells. The revealed correlations provide useful guidelines for designing novel copolymers based on extended TTATATT units for efficient organic photovoltaics.

Despite of design of materials with almost ideal optoelectronic properties, optimization of active layer morphology remains the bottle-neck on the way towards highly efficient devises. Moreover, morphology of blended photoactive layer is often metastable, that lead to the fast decrease of efficiency under operation conditions.

To solve this problem, one could connect acceptor and donor component by chemical bond. This approach lead to single-material architecture of solar cells. In such devises the size and arrangement of domains are predetermined by chemical structure of materials. The formation of pure and continuous domains is crucial in order to prevent recombination of charge carriers.

In this work, we enhance the immiscibility of donor and acceptor fragments by implementation of hydrophilic-hydrophobic interactions between solubilizing chains. Namely, keeping the donor part (P3HT) unchanged, we vary the nature of side-chains in the acceptor part of conjugated polymers. Formation of ordered structures in polymer thin films depends strongly on both the type of solubilizing chains and the thermal annealing as was revealed by AFM.

Speaker: Meruyert Karim, Center for Electrochemical Energy Storage

Title: Solid-state synthesis of nasicon type electrolyte

Abstract: All-solid-state batteries using ceramic electrolytes have attracted great interests due to their good chemical stability, high ionic conductivity, and superior safety which have been considered as the ultimate safe batteries. The Li1+xAlxTi2-x(PO4)3 (LATP) considered to be excellent candidate as solid electrolyte for energy storage application that have possibility to upgrade energy storage materials to the next level. It has been distinguished with very promising with very high lithium-ion conductivities (up to bulk 3 × 10−3 S cm−1, grain boundary 9 × 10−4 S cm−1, total 7 × 10−4 S cm−1). Therefore, it has great potential as solid electrolytes applied in all-solid-state lithium-ion batteries (LIBs). Particle size plays an important role on conductivity of crystalline electrolytes, and usually reduction on particle size favors improved ionic conductivity. There are various methods to synthesize LATP such as solid-state reaction, co-precipitation, sol-gel, and melting-quenching methods. The synthesis of LATP via solid-state chemistry is much documented. Thanks to the large choice in the raw material nature and synthesis parameters, solution chemistry favors the preparation of powders with controlled composition and morphology.