Research On Polymer Solar Cells Based On Mixed Au Nanoparticles-induced Localized Surface Plasmon Resonance

Sixty years ago, Bell laboratory firstly discovered a solar cell,which is a photovoltaic device converting light into electrical energy, marking that human entered into a new energy era. In the last several decades, traditional inorganic solar cells developed rapidly with power conversion efficiency varied from an initial 6% researched by Bell laboratory to about 40%, occupying about ninety percent of solar cell market. However, high cost, light decay and toxic characteristics seriously restrict the application of inorganic solar cells.Polymer solar cells have drawn worldwide attention in recent years for its low price, wide material sources, simple manufacture technique, flexibility and large-area. In this thesis we utilize surface plasmons to improve donor’s a bsorption and thus expolre its influence on solar cell’s with common P3HT:PC61BM or high performance PTB7:PC71BM bulk heterojunction.Surface plasmons are collective oscillation of free electrons under an excition of illumination, thus generating local field enhancement nearby the surface plasmons. The absorption in solar cells will be improved when the oscillation frequency of surface plasmons matches with the absorption wavelength of the active layer. In this thesis we synthesized mixed gold nanoparticles(Au NPs) with a seed-mediated growth method, generating a wide absorption spectrum of 400-1000 nm and three localized surface plasmon resonance(LSPR) peaks of 525, 575, and 775 nm. The as-synthesized Au NPs exhibit a quite good spectrum overlap with absorption spectra of P3 HT and PTB7. Doping these Au NPs into hole extraction layer with an optimal doping concentration of 4.5 vol%, the device shows best performance. The short-circuit current density and power conversion efficiency(PCE) improve 20.54% and 21.2%, respectively, in the P3HT:PC61BM-based solar cell and 17.3% and 19.8%, respectively, in the PTB7:PC71BM bulk heterojunction one. Our analysis shows that localized surface plasmon resonance and scattering of Au NPs to the incident sunlight mainly improve the absorption of the active layer. In addition, the enhancement of transportation ability on hole-extraction layer is another reason to improve the device performance.