The improvement of solar cell performance in the near-infrared (near-IR) region is an important challenge to increase power conversion efficiency under one-sun illumination. PbS quantum-dot (QD)-based heterojunction solar cells with high efficiency in the near-IR region were constructed by combining ZnO nanowire arrays with PbS QDs, which give a first exciton absorption band centering at wavelengths longer than 1 μm. The morphology of ZnO nanowire arrays was systematically investigated to achieve high light-harvesting efficiency as well as efficient carrier collection. The solar cells with the PbS QD/ZnO nanowire structures made up of densely grown thin ZnO nanowires about 1.2 μm long yielded a maximum incident-photon-to-current conversion efficiency (IPCE) of 58% in the near-IR region (@1020 nm) and over 80% in the visible region (shorter than 670 nm). The power conversion efficiency obtained on the solar cell reached about 6.0% under simulated one-sun illumination.

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For improvement of solar cell performance, it is important to make efficient use of near-infrared light, which accounts for ∼40% of sunlight energy. Here we introduce plasmonic Ag nanocubes (NCs) to colloidal PbS quantum dot/ZnO nanowire (PbS QD/ZnO NW) bulk-heterojunction solar cells, which are characterized by high photocurrents, for further improvement in the photocurrent and power conversion efficiency (PCE) in the visible and near-infrared regions. The Ag NCs exhibit strong far field scattering and intense optical near field in the wavelength region where light absorption of PbS QDs is relatively weak. Photocurrents of the solar cells are enhanced by the Ag NCs particularly in the range 700-1200 nm because of plasmonic enhancement of light absorption and possible facilitation of exciton dissociation. As a result of the optimization of the position and amount of Ag NCs, the PCE of PbS QD/ZnO NW bulk-heterojunction solar cells is improved from 4.45% to 6.03% by 1.36 times.

Temperature effects of CH 3 NH 3 PbI 3 perovskite solar cells having simple planar architecture were investigated on the crystal structure and photovoltaic performance. The obvious changes in the CH 3 NH 3 PbI 3 crystal structure were found by varying the temperature as a consequence to the augmentation in lattice parameters and expansion of the unit cell. The expansion of the crystal gave a serious influence on the performance of the solar cells, where the differences in the coefficients of the thermal expansion (CTEs) together with the lattice mismatch between TiO 2 and perovskite materials might cause interfacial defects responsible for the deterioration in the photovoltaic performance. Interestingly, the hysteresis in the cubic phase is very small because of the less distorted angles of the CH 3 NH 3 PbI 3 structure against the temperature fluctuation.Perovskite solar cells based on CH 3 NH 3 PbI 3 have attracted enormous attention in the last few years 1 due to their rapid improvement and high certified efficiencies over 20%.2 The architectures of the devices have been categorized to mesoscopic structure or simple planar heterojunction, 3 and the devices exhibit large hysteresis in JV characteristics especially in the planar structure. 4 The solar cells present a big mismatch in the power conversion efficiency (PCE) from forward (short circuit to open circuit) and reverse scan (open circuit to short circuit), and correct estimation of the PCE has been a controversial matter in recent past. 5 Several hypotheses have been proposed to be the origin of the hysteresis in planar architecture, such as ferroelectric proprieties of CH 3 NH 3 PbI 3 , 6 ion migration inside perovskite layer, 7 chemical and structural changes in the materials, and interfacial contact between the layers.8 However, the mechanism responsible for the anomalous hysteresis remains unclear.Another possible factor of the hysteresis is the interfacial contact and lattice mismatch between compact TiO 2 and perovskite layer.9 This interface may cause the temporal delay of the JV characteristics due to rearrangement of the interface under external bias and illumination. In fact, large decrease of hysteresis has been shown by modification of the compact TiO 2 layer using fullerene derivatives (C 60 , 60-PCBM).10 In this case, there is no lattice mismatch as the inorganic interface of the crystalline. Petrozza et al.10b also showed that allowing the TiO 2 interface to rearrange under voltage bias produces a similar injection rate to that of PCBM contact. One factor that affects the interfacial properties is ion accumulation, as shown by the large capacitance associated with electrode polarization.11 From theoretical calculations, it has been found that the migration of defects originated from the diffusion of iodide vacancies or high orientation of CH 3 NH 3 + is able to modify the interface. 12 In addition, CH 3 NH 3 PbI 3 undergoes several crystal phase transitions when the temperature of the solar cell is changed. 13 Recently, several devices...

A compact TiO 2 interlayer between fluorine-doped tin oxide (FTO) and perovskite in planar heterojunction perovskite solar cells is essential for effective charge extraction and minimized recombination. The electrical property of the interface of the perovskite layer with the compact TiO 2 layer is thus important for achieving high power conversion efficiency in the perovskite solar cells. The motivation for the present study was to improve cell performance by improving the property of the TiO 2 / perovskite interface. Interestingly, a remarkable enhancement in cell efficiency was achieved by treatment of the compact TiO 2 layer with TiCl 4 and UV(O 3 ).Organometal halide perovskites (CH 3 NH 3 PbI 3 ) have become a new attractive photovoltaic material due to their remarkable optical and electronic properties, and impressive power conversion efficiencies. In a very short time, perovskite-based solar cells have shown a continuous rise in cell power conversion efficiency, from less than 4% in 2009 1 to over 19% in 2014 for both meso-and planar-architectures. 2,3 In the early stages, the perovskite solar cells were fabricated based on the classic mesostructure dye-sensitized solar cells where perovskite functions as light absorber.1,4 On the other hand, due to the ambipolar charge-conductivity of this material, a simple architecture can be adopted, such as a planar pn heterojunction solar cells. 5,6 These types of solar cells, which are similar to organic polymer solar cells, are very attractive for potential commercialization because of simplicity of the device structure. The standard planar structure perovskite solar cells consist of a perovskite layer sandwiched between two charge transport layers: a thin compact TiO 2 layer and a 2,2¤,7,7¤-tetrakis(N,N-di-p-methoxyphenylamine)-9,9¤-spirobifluorene (spiro-OMeTAD) layer. In such heterojunction structures, morphologies of perovskite thin film and all interfacial connections play an important role in improving the cell performance. In addition, quality of the compact layer is another important factor that affects cell performance. Recent study 7 has shown that electron transfer is significantly improved by modifying compact TiO 2 layer with fullerene (C60-SAM) and hence, the cell performance is enhanced. This can be attributed to several aspects, better adhesion between compact TiO 2 layer and perovskite active layer improving the contact resistance and charge transfer reducing back charge recombination. 8 We have investigated here alternative methods for interface engineering of compact TiO 2 layer, TiCl 4 , and UV(O 3 ). The TiCl 4 treatment has been mostly studied in dye-sensitized solar cells (DSCs) for treatment and surface modification of the mesoporous TiO 2 layer.912 On the other hand, UV(O 3 ) treatment is a wellestablished cleaning method to remove organic contaminants from different surfaces increasing the wettability. 1319In this study, we report the influence of surface treatment of the compact TiO 2 layer with TiCl 4 and UV(O 3 ) on the cell performan...