| As two kinds of3rd generation photovoltaic devices, dye-sensitized solar cells (DSCs) and organic-inorganic perovskite solar cells (PSCs) have been regarded as very promising solar cells due to their simple procedures, high theory power conversion efficiency (PCE) and low-cost. With the continuous efforts from worldwide researchers, the PCEs of DSCs and PSCs have been updated to13%and19%, respectively.As key components, the counter electrode (CE) of DSCs and the back electrode of PSCs are used to collect electrons from the external circuit, and more importantly, catalyze the reduction of redox mediators in electrolyte and extract holes, respectively. Pt is the most widely used CE catalyst in DSCs. Au and Ag are the most widely used back electrodes in PSCs. However, there are serious problems in using of Pt, Au and Ag. Firstly, the scarcity and high cost of noble Pt, Au and Ag cannot meet the needs of mass industrial production. Secondly, Pt and Ag can be corroded by I-/I3-" electrolyte and organolead halide, respectively, thereby leading to poor stability of the photovoltaic device. Therefore, the development of high-performance, low-cost,.corrosion-resistant, non-precious metals catalysts and back electrode are highly desirable. Meanwhile, investigation of the role, catalytic mechanism and influencing factors for cell materials in photovoltic devices is needed to provide some guiding significance for development of new materials.Firstly, high-efficiency and low-cost tungsten oxides CEs were exploited. The influence of chemical composition, morphology and surface structure in tungsten oxides CEs on catalytic activity and photoelectric property were investigated in detail. To further reduce the cost and improve the stability, Pt-free and ITO-free flexible CEs based on low-cost carbon materials were successfully prepared. Their catalytic activity in quasi-solid electrolyte and photoelectric property in flexible quasi-solid DSCs were investigated. Low-temperature conductive carbon paste for PSCs was prepared by a considerate route of solvent exchange. HTM-free and metal-free mesoscopic heterojunction perovskite solar cells (MHJ-PSCs) and planar heteroj unction perovskite solar cells (PHJ-PSCs) based on low-temperature processed carbon back electrode were constructed as well as investigated systematically in terms of photoelectric property, separation of interface electron-hole pairs, collection of photo-generated carriers, as well as long-term stability.1. Development of tungsten oxide nano-materials and the study of their application in DSCs(1) New type WO2.72CEs catalytic materials were developed. Different from the reported non-Pt CEs, WO2.72CEs exhibited good performance of catalytic activity and DSCs for four kinds of redox couples. In addition, the match relationships between CEs and redox couples were observed as well.(2) By a facile and template-free approach of the solvothermal, WO2.72nanowires (NWs) were controllable synthesized. Compared with those with three-dimensional hierarchical structures, WO2.72NWs demonstrated two significant advantages:i) favorable to the fast transport of electrons and the exposure of active sites due to the oriented growth of WO2.72NWs along [010]; ii) beneficial to the interfacial contact and the diffusion of electrolyte within interlaced WO2.72NWs network. Thus, the NWs CEs exhibited good performances of catalytic activity and DSCs not only towards I-/I3-redox couple but also towards large-volume cobalt complex and ferrocenium redox mediators with low diffusion coefficients.(3) The catalytic active site in WO2.72NWs was further investigated. The results showed that surface oxygen vacancies (SOVs) could serve as catalytic active sites for reducton reaction in I-/I3-redox couples. The PCEs of DSCs based on WO2.72NWs decreased notably when SOVs were filled.2. Development of carbon back electrode and the study of their application in HTM-free and Metal-free heterojunction perovskite solar cells(1) Low-temperature processed carbon back electrode was developed. The influence of carbon back electrode thickness on conductivity and the PSCs performance were investigated systematically. Interficial electron-hole separation and collection were also investigated deeply. The key reason for enhanced stability of photovoltic device based on carbon back electrode was investigated. The result showed that the surface of carbon back electrode was very hydrophobic, thus beneficial to suppresse the damage of external moisture to three dimensional crystal structure of the perovskite. The PSCs based on carbon back electrode exhibited better stability in air and moisture:there was almost no decrease in PCE after2000h. Above results provided some foundation to the fundamental research, strategy in improving the stability and application of PSCs as well.(2) Low-temperature and all-solution processed ZnO/CH3NH3Pbl3/C planar heterojunction perovskite solar cells (PHJ-PSCs) were constructed. The relationships between structure and properties were investigated systematically. PCEs of rigid PHJ-PSCs were close to the value of reported HTM-free mesoscopic heterojunction perovskite solar cells based on Au back electrode. The flexible devices exhibited excellent anti-bending performance. This kind of low-temperature processed low-cost PSCs with simple architecture and procedure open a new way for application of flexibale solar cell. |
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