Polymer solar cells undoubtedly hold tremendous potential for solutionprocessable, inexpensive photovoltaics on flexible plastic substrates. 1Ϫ5 The most promising organic photovoltaics (OPVs) are based on random dispersion of acceptors in the form of organic or inorganic nanostructures within a conjugated polymer matrix, which acts as the donor phase. The interfaces at the acceptor nanostructures and the donor host polymer matrix create bulk heterojunctions (BHJs), which provide a large number of sites for charge separation and bicontinuous pathways for efficient carrier transport. 6Ϫ8 Although numerous combinations of acceptors and donors have been reported, 9Ϫ14 the most popular BHJ polymer solar cells consist of poly(3-hexylthiophene) (P3HT) and fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) blends. The mechanisms for achieving high photovoltaic efficiencies in excess of 6% in P3HT:PCBM BHJ devices are well-established. 15 However, several key components remain unresolved and must be addressed if the theoretical efficiencies of ϳ10% are to be realized. 16 For example, in a simple BHJ device, both the donor and acceptor phases are in direct electrical contact with the cathode and anode electrodes, leading to recombination of carriers and current leakage. To minimize such detrimental effects, electron blocking and hole transport layers (HTLs) are deposited on top of the transparent and conducting indium tin oxide (ITO) anode. HTLs must be wide band gap p-type materials, and several inorganic materials such as V 2 O 5 and MoO 3 17 have been reported with NiO being the most effective, yielding efficiencies greater than 5%. 18 However, inorganic HTLs are deposited using vacuum deposition

In this article, we demonstrate a semitransparent inverted-type polymer solar cell using a top laminated graphene electrode without damaging the underlying organic photoactive layer. The lamination process involves the simultaneous thermal releasing deposition of the graphene top electrode during thermal annealing of the photoactive layer. The resulting semitransparent polymer solar cell exhibits a promising power conversion efficiency of approximately 76% of that of the standard opaque device using an Ag metal electrode. The asymmetric photovoltaic performances of the semitransparent solar cell while illuminated from two respective sides were further analyzed using optical simulation and photocarrier recombination measurement. The devices consisting of the top laminated transparent graphene electrode enable the feasible roll-to-roll manufacturing of low-cost semitransparent polymer solar cells and can be utilized in new applications such as power-generated windows or multijunction or bifacial photovoltaic devices.

This paper presents an innovative approach to fabricating controllable n-type doping graphene transistors with extended air stability by using self-encapsulated doping layers of titanium suboxide (TiOx) thin films, which are an amorphous phase of crystalline TiO(2) and can be solution processed. The nonstoichiometry TiOx thin films consisting of a large number of oxygen vacancies exhibit several unique functions simultaneously in the n-type doping of graphene as an efficient electron-donating agent, an effective dielectric screening medium, and also an encapsulated layer. A novel device structure consisting of both top and bottom coverage of TiOx thin layers on a graphene transistor exhibited strong n-type transport characteristics with its Dirac point shifted up to -80 V and an enhanced electron mobility with doping. Most interestingly, an extended stability of the device without rapid degradation after doping was observed when it was exposed to ambient air for several days, which is not usually observed in other n-type doping methods in graphene. Density functional theory calculations were also employed to explain the observed unique n-type doping characteristics of graphene using TiOx thin films. The technique of using an "active" encapsulated layer with controllable and substantial electron doping on graphene provides a new route to modulate electronic transport behavior of graphene and has considerable potential for the future development of air-stable and large-area graphene-based nanoelectronics.

A heterojunction photodiode with NIR photoresponse using solution processable pyrite FeS(2) nanocrystal ink is demonstrated which has the advantages of earth-abundance and non-toxicity. The device consists of a FeS(2) nanocrystal (NC) thin film sandwiched with semiconducting metal oxides with a structure of ITO/ZnO/FeS(2) NC/MoO(3) /Au, which exhibits an excellent photoresponse with a spectral response extended to NIR wavelengths of up to 1150 nm and a high photocurrent/dark current ratio of up to 8000 at -1 V under AM1.5 illumination (100 mW cm(-2) ).

Using cross-sectional scanning tunneling microscope (XSTM) with samples cleaved in situ in an ultrahigh vacuum chamber, this study demonstrates the direct visualization of high-resolution interfacial band mapping images across the film thickness in an optimized bulk heterojunction polymer solar cell consisting of nanoscale phase segregated blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). We were able to achieve the direct observation of the interfacial band alignments at the donor (P3HT)-acceptor (PCBM) interfaces and at the interfaces between the photoactive P3HT:PCBM blends and the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) anode modification layer with an atomic-scale spatial resolution. The unique advantage of using XSTM to characterize polymer/fullerene bulk heterojunction solar cells allows us to explore simultaneously the quantitative link between the vertical morphologies and their corresponding local electronic properties. This provides an atomic insight of interfacial band alignments between the two opposite electrodes, which will be crucial for improving the efficiencies of the charge generation, transport, and collection and the corresponding device performance of polymer solar cells.