Study On Subphthalocyanine/C₆₀ Organic Solar Cells

Recently, photovoltaic cells （OPV） has become one of common means to exploitsolar energy. Among various kinds of cells, organic photovoltaic cells have caughtworld’s attention due to their distinctive advantages: low cost, abundant kinds ofmaterials and simple fabrication process. However, their significantly lower efficiencycompared with silicon-based solar cells remains a problem yet to be conquered.As a new material in the field of organic photovoltaic cells, subphthalocyanine（SubPc） has many promising properties. With the same basic properties asphthalocyanine, SubPc possesses lower Highest Occupied Molecular Orbital （HOMO）energy levels, and provides possibilities of achieving high open-circuit voltages. Thefollowing are the main experiments using SubPc as an electron donor material:For the first part, a solar cell with SubPc as a donor and C₆₀as an acceptor wasfabricated. Based on above structure, PEDOT:PSS used as an anode modification layerand Bphen used as an exciton selective layer were inserted to discuss their impact on thecell performance. The results show that when both were used at the same time, theperformance of the cells reach the best value, with a short-circuit current-density （Jsc） of2.88mA/cm², open-circuit voltage （Voc） of0.79V and power conversion efficiency （PCE）of0.73%.For the second part, pentacene was introduced into OPV cells to increase thetransport efficiency of excited holes for its excellent hole-transport properties. Firstly,pentacene as a hole-transport layer was inserted between PEDOT:PSS and SubPc invarious thickness to discuss the influence on the cell. Results suggest a highest increaseof Jscfrom2.46mA/cm²to4.23mA/cm²at4nm of pentacene, however Vocdrops from0.74V to0.31V, resulting in a decrease of PCE. Afterwards, pentacene is insertedbetween SubPc and C₆₀, resulting in a fatal drop of efficiency with the increase ofthickness of pentacene, reaching less than0.01%at6nm. Finally, pentacene and SubPcwere blended to form a mixed donor layer. Comparing with the device ofpentacene:SubPc/C₆₀, the device with a pentacene:SubPc/SubPc/C₆₀architecture had obvious increase in Jscand Vocas well as the46%increase of PCE. The conclusion canbe drawn that an extra layer of SubPc between the blend and C₆₀can enhance theperformance of OPV at a high degree.For the third part, the phosphorescent material （pbi）₂Ir（acac） was used as donormaterial as it has the same HOMO level as SubPc. Designed a three-layer cell asSubPc/（pbi）₂Ir（acac）/C₆₀， compared with two-layer cells as （pbi）₂Ir（acac）/C₆₀andSubPc/C₆₀. Although the three-layer cell got a low PCE=0.05%, the experiments hadpaved the way for further optimize the performance based on phosphorescent materialas a photoactive material.