Center for Functional Nanomaterials Seminar

Polymer solar cells (PSCs) provide special opportunities for low-cost, printable, light-weight, flexible, and portable energy sources. For the past few years, a great advance to improve the efficiency of polymer solar cells has been achieved owing to development of new materials, understanding of organic semiconductor physics and advancement in the device optimization including interface engineering. As a result, the power conversion efficiency (PCE) has continuously increased to its current value of higher than 7%. Nevertheless, further development of PSCs is still needed for commercialization, which requires the PCE higher than 10%. The most critical disadvantages of PSCs are lower efficiency and poorer durability as compared to inorganic-based solar cells.

To enhance the PCE with the reduction of the charge recombination and the increase of fill factor, we synthesized C60-end capped poly(ethylene glycol) and added into the P3HT/PCBM blend to control the vertical composition gradient across active layer.

Some efforts have been devoted to improve the long-term durability of PSCs in our laboratory: (i) use of compatibilizer to control and suppress the macro-phase separation in active layer, (ii) use of deep HOMO materials to prevent oxidative degradation, and (iii) use of non-acidic or less acidic hole transport layer-material than PEDOT:PSS. Particularly, it has been observed that the use of donor-acceptor type diblock copolymer as compatibilizer remarkably improves the long-term thermal stability of PSCs based on P3HT:PCBM.

Recently, we developed a new fabrication method compatible with continuous solution process. Although spin coating is very useful for fabricating very thin and homogeneous film and successful for controlling the film thickness, the spin-coating process has several detrimental problems in its application to mass production. In order to overcome these problems, a novel coating process, roller printing, has been developed.