The Manipulation Of Photon-electron Conversion In Organic Solar Cells

Organic solar cells have attracted much attention because of its low cost, simplefabrication process and large area production. So far, power conversion efficiency(PCE)has been achieved over10%using a tandem structure. However, it is still of importanceto get further improvement for the commercialization. The Photon-Electron conversionprocess is very important for device performance, which includes light absorption,exciton generation, exciton dissociation and charge collection. Here, in order to improvecell performance, down-shifting and singlet fission were introduced into the organicsolar cells to regulate photo-electron process. The results show that down-shifting canimprove short-circuit current(Jsc) and PCE simultaneously.In this work, organic solar cells were fabricated using P3HT:PCBM, P3HT: ICBA,and also CuPc/C60as the active materials by spin-coating or vacuum deposition process.Detailed works are as follows:(1) The C545T:Alq3with different doping concentration was introduced intoP3HT:PCBM and P3HT:ICBA based organic solar cells as down-shifting fluorescencesensitizer and electron transport layer(ECL). Short wavelength photons ranged from300nm-400nm were shifted to longer wavelength, where the active layer shows strongabsorption. Compared to reference device, the photocurrent improved from10.48mA/cm2and12.03mA/cm2to11.96mA/cm2and12.53mA/cm2, PCE improvedfrom3.28%and5.58%to3.82%and6.01%. The results were shown in current-voltagecurves and external quantum efficiency. However, the photocurrent of CuPc/C60basedsolar cell was decreased when the sensitizer was introduced, we attributed it to themismatched energy levels between Alq3and C60.(2) The Ir(ppy)3:Alq3film with different doping concentration was introduced into P3HT:PCBM based organic solar cells as down-shifting phosphorescence and electrontransport layer(ECL). In this experiment, there is no obvious improvement in deviceperformance, which could be attributed to inefficient energy transfer between Ir(ppy)3and Alq3. These results also demonstrated that matched energy level between host andguest material is very important in down-shifting progress.(3) Singlet fission material—pentacene by vacuum deposition progress was used inthe small molecule organic solar cell with structure ofITO/P3HT/Pentacene/C60/Bphen/Al. Firstly, device performance was optimized throughchanging the thickness of the film. Then, singlet fission phenomenon was evidenced byphotocurrent change applied magnetic field, which white light and650nm laser wereutilized as light source.