Study Of High Efficiency PCDTBT-based Polymer Solar Cells

Organic polymer solar cells for its low cost, flexibility, easy to use, simple process hasgot wide attention. At present, the power conversion efficiency of polymer solar cells hasreached8.62%, which indicate the polymer solar cells will have more extensive applicationprospects. In this paper, high efficiency polymer solar cell is fabricated with loe-bandgappolymer PCDTBT as electron donor material. We also discuss the influence of differentactive layer thickness, film growth process and thin silver layer on the performance ofpolymer solar cells.We fabricated organic polymer solar cells with (PCDTBT)(Poly [N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]) which has lowerbandgap compared with P3HT as electron donor material and (PC70BM)([6,6]-phenylC70-butyric acid methyl ester) instead of PC60BM, which has wider spectra absorption aselectron accepter. The power conversion efficiency (PCE) has enhanced to5.65%bycontrolling the growth rate and the environment of active layer. Then we optimized thethickness of active layer film, PCE was improved to5.84%with the circuit current density Jsc=14.2mA/cm2. The results demonstrated that even the optical spacer was not used, the activelayer can also have an higher absorption and further improved the PCE with the control ofgrowth rate and thickness of active layer. The result of this experiment make it is possible forus to produce organic solar cells with simplier fabrications and lower costs.On this basis, we inserted a Ag layer between ITO and PEDOT:PSS. Thus lights makeround trips between the thin film of Ag and the metal electrode which lead to higher externalquantum efficiency (EQE) together with a remarkable increase of short circuit current(Jsc).Then we optimized the thickness of Ag layer, PCE was improved to6.03%when the Jsc was15.0mA/cm2. This demonstrates that by building an optical resonant cavity, we can make abig improvement of the performance of polymer solar cells.Finally, we investigated the effects of Ag nanoparticles (NPs) on the performance oforganic solar cells. When the doping concentration of Ag NPs is5%, Jsc=13.8mA/cm2,PCE=5.61%, which is increased by approximately10%compared with no doping. Explainedas follows: a small amount of Ag nanoparticles doping can increase the light absorption of theactive layer and the migration of the electronic conductivity, thereby increased the shortcircuit current and conversion efficiency of polymer solar cells. However, when the doping concentration is too high, it is easy to formation of the gathering area of the electron (hole) inthe Ag particle surface, reducing the electron collection efficiency at the same time increasingthe electron-hole recombination probability. Thereby significantly reduced the performance.