| Organic solar cells based on conjugated polymer/fullerene have attracted considerable attention overthe past several years due to their low-cost, light-weight, roll-to-roll manufacturing, and large-areaprocessability. Recent remarkable progress has been made in conversion efficiency, approaching10%.Generally, the photovoltaic device performance is influenced by absorption, exciton diffusion, chargeseparation and charge collection. It is worth noting that the interface between the metal electrodes and theactive organic layer plays a crucial role in the efficient charge collection from the active organic layer. Thus,an ideal electrode must be highly conductive and stable chemically. Indium-tin oxide (ITO) is most widelyused as transparent conductive anodes in organic solar cells. In the conventional approach, a conductingpolymer, polyethylenedioxythiophene doped with polystyrenesulfonate (PEDOT:PSS), is commonly usedto modify ITO to improve hole extraction. However, PEDOT:PSS is known to be hygroscopic and acidic,which will cause corrosion of the anode and degradation of device performance. In this work, themodification of the interfaces of anode or cathode in organic solar cells based on poly (3-hexylthiophene)(P3HT) and [6,6]-phenyl C61-butyric acid methy lester (PCBM) were investigated.In the first section, the progress in solar cells was reviewed. The principle of organic solar cells wasintroduced. The purpose and significance of this work were developed.In the second section, the effects of the slow growth of active layer of P3HT:PCBM on theperformance of bulk heterojunction polymer solar cells were investigated. The optimal growth duration ofP3HT:PCBM films was obtained after we systematically changed preset time before annealing blendedfilms. The result indicates that when P3HT:PCBM film was put in petridish for60min before annealingblended films, the power conversion efficiency of polymer solar cells reached3.94%, the fill factor reached52.88%, the electric current density reached13.49mA/cm~2. However, the power conversion efficiency ofpolymer solar cells based on P3HT:PCBM with fast growth was only3.58%, the fill factor was only52.88%, the electric current density was only12.99mA/cm~2. The improved power conversion efficiency is attributable to the reasonable phase-separation between P3HT and PCBM blended film, which boostedcarriers transport and hop.In the third section, anodes in heterojunction solar cells based on P3HT:PCBM were modified byplatinum nanoparticles (NPs). The open-circuit voltage (Voc) of the cells was increased compared with thereference cell without Pt NPs. An enhanced power conversion efficiency of~12%was obtained for theoptimum sputtering deposition duration of10sec. A double junction model of the Schottky junction andthe p-n junction is proposed to describe the frequency dependence of the capacitance in the modified cell.The formation of the front Schottky junction allows efficient collection of holes from the active layer, andenhances the Voc. Moreover, the air stability of organic solar cells was improved. The modification of ITOwith Pt NPs shows promise as a technique for fabrication of high-efficiency stable photovoltaic devices.In the fourth section, the modification of cathode in organic solar cells was investigated usinggraphene and lithium fluoride (LiF). Graphene and LiF were co-vapor-deposited as the cathode buffer of anorganic solar cell. The open circuit voltage of solar cell with cathode modified by LiF:G was0.57V, shortcircuit current density reaches11.37mA/cm~2, PCE of3.45%, FF of53.3%. All performance parameterswere better than those of the reference solar cell without grapheme.In the fifth section, summary and outlook for this present work were given. |
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