The Application Of Functional Fullerene Materials In Solar Cells

In this paper, two novel triblock functional fullerene derivatives were reasonably designed and synthesized in order to solve the problems which exist currently when fullerene derivatives applied as acceptor materials in bulk heterojunction polymer solar cells（BHJ PSCs） and as modified layer of electron transport layer（ETL） in organic-inorganic metal halide perovskite solar cells. The induced cyano-groups and long alkoxy chains can optimize the surface morphology through supramolecular assembly effect and finally improve the PCE when using in BHJ PSCs, They also can effectively passivste the trap sites of ETL which is prepared from metal oxide and eventually improve the PCE and hysteresis effects. More detailed research and conclusions are showed below:1. We have successfully designed and synthesized a new fullerene derivative PCBB-CN-C8 which consists of styrene cyano group, tri（octyloxy）benzene and C₆₀. It can firstly utilize its supramolecular effect to self-assemble into ordered structure, and then induce the donor material（P3HT） to crystalize into long-range ordered lamellar structure through long alkoxy chains, finally establish nanoscale phase-separated interpenetrating network morphology during spinning coating process. The BHJ PSC based on the blend films of P3 HT and PCBB-CN-C8 without any external treatment process exhibited excellent photovoltaic performance with a PCE higher than 3.6 %. For all we know, the PCE which is higher than 3.51 % is the highest photovoltaic performance among the P3HT-based PSCs without thermal annealing. Besides, the intermolecular interaction of PCBB-CN-C8 was enhanced owing to the import of cyano-group, as a result the glass transition temperature（Tg） was increased which inhibited the diffusion of PCBB-CN-C8 and maintained a good morphology of active layer when heating. After thermal annealing, the PCE of the blend film reached 4.20 % which is even comparable to the highest PCE of the P3HT-based PSCs reported by sequential two-step treatments.2. Another multifunctional fullerene derivative PCBB-2CN-2C8 which contains two electron-withdrawing cyano-groups and two long alkoxy chains was also designed and synthesized successfully. The introduced dioctyloxy chains and cyano-groups can remarkably enhance the hydrophobicity of PCBB-2CN-2C8. This will not only be good for improve its solvent resistance to the solution of perovskite precursors, but also be easer to obtain larger perovskite crystals on the hydrophobic PCBB-2CN-2C8 surface, then finally fabicrate integrated perovskite solar cells. Besides, when using PCBB-2CN-2C8 to modify the ETL（TiO₂）, It can also assemble on the surface of TiO₂ to pacify the oxygen vacancy, and then significantly reduce charge recombination caused by surface traps, eventually dramatically improve the performance and hysteresis effects as well as the lifetime of the device. In the end, the V_OC and FF was increased from 0.99 V, 72.2 % to 1.06 V, 79.1 %, respectively, and a 20.7 % enhancement in PCE was obtained.