Carbazole-Based Hole-Transport Materials for Efficient Solid-State Dye-Sensitized Solar Cells and Perovskite Solar Cells

摘要

With the recent rise in awareness of environmental and energy issues, renewable energy sources are given more and more attention. Looking at photovoltaics, dye-sensitized solar cell (DSC) is considered to be a promising candidate as a large-area and low-cost renewable energy sourcei In this rapidly developing field, the identification of efficient electrolytes to improve efficiency is of great importance for the promotion of DSCs. So far, the best conversion efficiency of 13% have been obtained with prophyrin-based dyes used together with the Co(Ⅱ/Ⅲ)-tris(bipyridyl) complexes as redox couple in liquid electrolytes. Despite the fact that considerable progress has been made in this field of research, the risk of leakage associated with the volatile nature of a liquid electrolyte, together with fundamental stability issues represent significant limitations for the commercialization of these devices. A significant part of the efforts made in this field has been devoted to the optimization of the fabrication of solar cells based on solid-state hole-transport materials (HTMs) as the formal electrolyte system responsible for the regeneration (reduction) of the sensitizing dye molecules. To date, the highest efficiency reported amounts to 7.2% for solid-state dye-sensitized solar cells (ssDSCs) and 15.4% for perovskite solar cells (PSCs); both champion results have been achieved using Spiro-OMeTAD as the HTM. However, previous studies have demonstrated that the onerous synthesis and low charge-carrier mobility of Spiro-OMeTAD significantly limit its potential of up-scaling for applications of ssDSCs and PSCs. Therefore, the development of a new generation of HTMs with low cost, facile synthesis and high charge-carrier mobility is of high priority. Carbazole-based derivatives have attracted much attention because of their interesting photochemical properties. Recent interest in the car-bazole derivatives has been caused by its good charge-transport function, which can be exploited in the molecular design of new types of HTMs in organic light-emitting diodes (OLED) and as electron donor group in organic sensitizers of D-π-A-type in DSCs. Another fascinating advantage is the versatility of the carbazole reactive sites that can be substituted with a wide variety of functional groups, allowing fine-tuning of its optical and electrical properties. Herein, we present on the design and synthesis of two novel carbazole-based, small-molecule organic HTMs denoted X51 and X19 (Figure 1) characterized by a straightforward synthetic route and high hole mobility, together with their successful application in ssDSCs and PSCs. One of the HTM- based, X51, devices exhibit high power conversion efficiencies (PCEs) amounting to 6.0% and 9.8% in dye sensitized and perovskite solar cells, respectively. These results are comparable to the PCEs of 5.5% and 10.2% obtained by using the well-studied champion HTM, Spiro-OMeTAD, under standard AM 1.5 solar light illumination of 100 mW·cm~(-2) intensity. To the best of our knowledge, this is the first report of a carbazole-based, small-molecule organic HTM that can challenge the state-of-the-art HTM Spiro-OMeTAD both in ssDSCs and PSCs.