The Study Of Photoconductive Cathode Interlayer Based On Dye Molecules Doped ZnO

Organic solar cells have attracted intensive research interest worldwide as they can be a potential supplementary source of potential low-cost, renewable energy. The power conversion efficiency(PCE) for lab-fabricated organic solar cells has surpassed 10%, which is the threshold for industrial production. However, the optimal conditions for lab-fabricated organic solar cells are not suitable for industrial production. The most important issue is that the thickness of the functional layers for lab-fabricated organic solar cells is very thin, especially for the interlayers, which are around 2~30 nm. It is difficult for the industrial production to print such thin film uniformly. Here, the doctoral degree candidate proposed the concept of photoconductive cathode interlayer and investigated the mechanism for the application of the thick photoconductive cathode interlayer in high performance organic solar cells, which may guide the design of thick film high-performance interface layer for industrialized production. The work of the thesis can mainly divide into four parts.In the firt part, we used Zn O/PBI-H double layer structure to make cathode interlayer and achieved high PCE in organic solar cells. The PBI-H modifying reduced the work function of Zn O and improved the contact between Zn O and the acitve layer. After thermal treatment, the N-Zn chemical bond formed between Zn O and PBI-H increased the combination of the two layers, which was beneficial to the electron transport from PBI-H to Zn O. The devices based on optimal condition of Zn O/PBI-H cathode interlayer and PTB7:PC71BM as the active layer showed PCE as high as 9.43%. In addition, the Zn O/PBI-H cathode interlayer was suitable for different material systems, the PCE for P3HT:PC61BM system increased from 3.51% to 4.78% and for PTB7-Th:PC71BM system increased from 8.33% to10.31%.In the second part, we used organic dyes doping Zn O to fabricate photoconductive cathode interlayer and improve the PCE of inverted organic solar cells(i OSCs). Due to the low doping concentration about 1%, the photoconductive cathode interlayer absorbed a quite small amount of light but showed highly increased conductivity. As shown in Zn O:PBI-H film, the conductivity of this film was 4.5×10-3S/m under the condition of the test of organic solar cells, moreover, the PBI-H doping increased the electron mobility and reduced the work function of Zn O film. The devices based on the Zn O:PBI-H phtoconductive cathode interlayer and PTB7-Th:PC71BM as the active layer showed PCE as high as 10.5%. More important is that the device performance changed slightly with the thickness of the photoconductive cathode interlayer changed from 30 nm to 60 nm, due to the high conductivity of the Zn O:PBI-H film. The thickness insensitive interlayer was of great importance to future industrial production. We also used some other organic dyes to dope Zn O to make photoconductive interlayer.In the third part, we presented an aqueous solution processed photoconductive cathode interlayer for high performance i OSCs by doping Zn O with a small amount of mild acidic aqueous soluble perylene bisimide derivative(PBI-Py). The photo-induced charge transfer process provided by PBI-Py doping of Zn O brings multiple advantages for the cathode interlayer, including significantly increased conductivity and electron mobility as well as reduced WF, which are crucial properties for an efficient cathode interlayer. These novel concept for improving charge transport property and WF may guide the development of a new generation of interfacial materials. The i OSCs based on the Zn O:PBI-Py photoconductive cathode interlayer and FBT-Th4(1,4):PC71BM active layer showed average PCE over 10% even when the thickness of the cathode interlayer and active layer was up to 100 nm and 300 nm, respectively. We successfully demonstrated the combination of environment-friendly processing approach, thickness insensitive device performance and high efficiency in one PSC, which take a giant step forward to the large production of OSCs.In the fourth part, we demonstrated the usage of pothoconductive cathode interlayer in ternary organic solar cells and a new approach of using near-NIR small molecule and high efficiency mid band gap polymers to fabricate high performance ternary blends OSCs. PCE improvement was seen in 10-70% DPPEZn P-TEH loading mixtures. The high composition tolerance is unique in multi-component OSC studies and a PCE > 11% is also rare. The extended absorption of the mixtures elevated the Jsc, addressing the major challenge in OSC research. Collateral benefits were seen in reducing recombination and enhancing charge extraction, all accounted for enhanced Jsc and FF. In a more detailed device performance map, 10-30% of DPPEZn P-TEH loading led to a linear enhancement in Jsc and FF; adding more DPPEZn P-TEH would lead to a reduction. When combined with GIXD studies, we suspect that in a low loading region(<30%), PTB7 served as effective matrix to host amorphous and crystalline DPPEZn P-TEH contents. This morphology would be disrupted at a higher DPPEZn P-TEH content, leading to isolated or segregated DPPEZn P-TEH domains. We noticed a reduction in hole-mobility and a longer carry extraction time for 50% blends, supporting this argument. Thus optimization at a host-guest mixing region is the key. Our results clearly demonstrated the great potential of the application of photoconductive cathode interlayer in high performance ternary OSCs.