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Abstract: We discovered that fringe structures of ZnO film in solar cells of inverted structures penetrate through the active layer made of low bandgap polymers. The ZnO penetration leads to leakage current of the solar cells. To prevent the ZnO penetration, the thin film morphology was modified. By changing the solvent and inserting TiO2 nanorods between ZnO film and the active layer, penetration can be avoided, so Rsh is improved from 110.3Ωcm2 to 374.7Ωcm2 and V oc from 0.36V to 0.66V. This result provides a promising route for employing low bandgap polymers to air-stable inverted structures with solution process. It is possible that inverted low bandgap polymer solar cells can achieve the goals of high performance and air stability. [Copyright &y& Elsevier]

Abstract: Stability is an essential issue in polymer solar cells for achieving commercially applicable devices. In this work, we report on a highly stable polymer solar cell, based on an inverted structure with the active layer sandwiched between a pair of metal-oxide buffer layers and an inherently air-stable conjugated polymer, a-PTPTBT. After interface modification, the unencapsulated device can retain power conversion efficiency without apparent degradation even after six months of storage in ambient conditions. This device''s excellent stability is attributed to the air-stable and chemically stable conjugated polymer, as well as the environmentally robust metal oxides used as the interfacial layers. To further improve the device performance, cathode-side interface modification was also carried out. After the insertion of the TiO2 nanorod interlayer between the ZnO thin film and the active layer, the device efficiency can be successfully increased from 3.3% to 4.1%. The future application of this materials system in inverted structures needs efforts devoted to morphology control and interface engineering to improve the device fill factor. The methodology applied here can serve as an effective strategy for fabricating highly air-stable devices with different materials systems. [Copyright &y& Elsevier]

Abstract: The selection of carrier transporting layer in polymer solar cells is an important issue because the nature and direction of carrier transport can be manipulated by inserting different functional layers in the device structure. In this work, we report a very efficient inverted polymer solar cell (PSC) system based on regioregular poly(3-hexylthiophene) and a n-type acceptor, bis-indene[C60]. With a pair of metal oxides and the insertion of TiO2 nanorods electron collecting layer between the ZnO thin film and the active layer, the device efficiency can be greatly improved. The contact area between the active layer and the electron collecting layer, as well as the thickness of active layer, can be increased with the incorporation of TiO2 nanorods. As a result, photocurrent can be enhanced due to more absorption of light and more charge separation interface. In addition, the larger contact area and the crystalline TiO2 nanorods provide a more efficient transporting route for the carriers to the cathode. The most efficient device demonstrated shows a high power conversion efficiency of 5.6% with the inverted structure. [Copyright &y& Elsevier]

Abstract: Bis-indene fullerene (ICBA) is a highly symmetric molecule that tends to diffuse and aggregate into larger clusters, resulting in a huge horizontal phase separation when the master solvent vaporizes, in addition to a significant drop in power conversion efficiency (PCE). We found that Poly(3-hexylthiophene) (P3HT): indene-C60 bisadduct (ICBA) blended with a high-molecular-weight polyvinylcarbazole (PVK) film could effectively prevent the clustering of ICBA crystalline molecules, thereby improving the phase separation. Furthermore, PVK dispersed the ICBA:P3HT active layer in a more uniform manner, increasing open circuit voltage (V oc ) and reducing photocurrent loss. As a result, the PCE of the device can be improved from 2.2% to 4.5%. [Copyright &y& Elsevier]

Abstract: We applied the horizontal electric field externally to improve the performances of organic solar cells based on the P3HT:PCBM heterojunction system. The treatment can orientate polymer materials and change the morphology of the active layer. Hence, the fill factor (FF) is enhanced from 63% to 67%. Furthermore, the treatment improves the morphology of the active layer. The root mean square (RMS) roughness of the active layer is increased and the contact areas between the layer and the electrode become larger, which raises current density (J SC) from 9.14mA/cm2 to 9.55mA/cm2. Therefore, the device applied with horizontal electric field has better performance and the power conversion efficiency (PCE) enhances from 3.04% to 3.46%. [Copyright &y& Elsevier]

Abstract: Molybdenum oxide (MoO X ) has drawn increasing attention in organic photovoltaic cells due to the large performance enhancement achieved in organic light emitting diodes. In this work, we report on inverted polymer photovoltaics (PVs) with solution-processed MoO X as anodic modification to enhance the performance of PVs. MoO3 is reduced to MoO X with x<3 after air-plasma treatment and then plays a role more closely to the thermally deposited MoO X , whose oxygen ratio is reduced during high temperature deposition. The reduced oxygen ratio provides more effective transport, thus enhancing the J SC of the devices. The PCE of the device with solution-processed MoO X is then enhanced to over 4%, which is comparable to that of thermally deposited MoO X . As a result, this work provides good compatibility for deposition of solution-process MoO X on top of polymer:fullerene blends in inverted polymer PVs to achieve better performance. [Copyright &y& Elsevier]