Study Of NiO Photocathode-based Mesoscopic Solar Cells Devices

Since the crucial contribution by Gratzel et al. in 1991, dye-sensitized solar cells (DSSCs) have attracted growing interests as low cost alternatives to the conventional inorganic photovoltaic devices. The implementation of an active photo-cathode with a photoactive anode opens the possibility to fabricate tandem DSSC devices, surpassing the Shockley-Queisser limitation for conventional n-type DSSCs. Accordingly, there is an increasing interest in development of p-type DSSCs. To date, most of p-type sensitizers use the conventional carboxylic acid groups as an anchoring group, which is not suitable for an efficient p-type sensitizer working mechanism. Thus, the ongoing search for suitable alternatives is prompted.The hybrid perovskite solar cell (PVSC) was initially discovered in a DSSC using a mesoporous TiO2 structure. Afterwards, solar cells using hybrid lead halide perovskite as light harvester have evidenced significant progress in the past few years. Currently, the certified efficiency for perovskite solar cells has surpassed 20% in lab-scale devices. Perovskite devices will be certainly benefited from new materials and device configurations, and thus, resolving some obstacles existing in the conventional cells, such as the current-voltage scan hysteresis. The elimination of photocurrent hysteresis in the inverted CH3NH3PbI3-based solar cells has been demonstrated by different research teams. Meanwhile, nickel-oxide (NiO)-based inverted PVSCs have also shown growing attention, due to its high stability and electrical conductivity.In this work, we systematically explored the preparation and optimization of NiO based p-type DSSCs and inverted PVSCs. The influence from the anchoring group on the p-type NiO has been well documented. Every interlayer in the NiO based inverted PVSCs has been well investigated. The photogenerated charge behavior has been carefully probed to illustrate the device working mechanism by using electrochemical impedance spectra, photovoltage/photocurrent decay, and current-voltage (J-V) analysis. The main contents of this thesis are listed as following:Two analogues to the widely-used P1 dye,4-(bis-{4-[5-(2,2-dicyano-vinyl)thiophene-2-yl]phenyl}amino) phenyl pyridine, coded as CW1 and (4-(bis-{4-[5-(2,2-dicyano-vinyl)thiophene-2-yl]phenyl}amino) benzene) phenyl pyridine, coded as CW2 were designed for p-type DSSCs, in which a pyridine ring is used as the anchor group instead of carboxylic acids. Besides considering the electron rich character and weak electron-withdrawing character for pyridine ring, we are also concerned that if there is a negative shift effect of VB of NiO semiconductor induced by surface protonation, just like what have observed in classical TiO2 DSSCs, cutting down the device photovoltage. The detailed investigation demonstrates that carboxylic acid groups may have an effect on negative shift of the valence band edge of NiO induced by surface protonation, which lowers the hole-injection process and the device photovoltage, while the pyridine ring works effectively without this problem. The p-DSSC based on the new sensitizer CW2 shows an over-all conversion efficiency of ?0.16%.P-type NiO electrode-based CH3NH3PbI3 PVSCs were fabricated, showing that significant power conversion efficiency (PCE) improvement from 4.88% to 6.13% by introducing a homogeneous and uniform NiO blocking interlayer fabricated with reactive magnetron sputtering method. The sputtered NiO layer exhibits enhanced crystallization, high transmittance and uniform surface morphology as well as a preferred in-plane orientation of (200) plane. The PCE of sputtered NiO based perovskite p-i-n planar solar cell can be further promoted to 9.83% when a homogeneous and dense perovskite layer is formed with a novel solvent-engineering technology, showing an impressive open circuit voltage of 1.10 V, a short-circuit current of 15.17 mA cm-2, and a fill factor of 0.59. This is about 33% higher than that of devices using the conventional spray pyrolysis NiO onto transparent conducting glass. These results highlight the importance of morphology- and crystallization-compatible interlayer towards high-performance inverted perovskite p-i-n planar solar cell and conclude a universal method to fabricate efficient NiO-based perovskite solar cell.The incorporation of spectrally tuned gold/silica (Au/SiO2) core/shell nanospheres and nanorods into the inverted perovskite solar cells (PVSC) leads a significant increase (-20%) in power conversion efficiency (PCE). The introduction of localized surface plasmons, which occur in response to electromagnetic radiation, have shown dramatic enhancements of exciton dissociation in Au/SiO2 nanorods-CH3NH3PbI2.85Br0.15 system. The well increased Eg of Br-based perovskites not only offers appropriable solar radiation window for surface plasmon resonance effect utilization, but also shows higher Vocs than pristine CH3NH3PbI3. Synchronized improvement in photovoltage and photocurrent leads to an inverted CH3NH3PbI2.85Br0.15 planar PVSC device with PCE of 13.7%. The spectral response characterization, time resolved photoluminescence, and transient photovoltage decay measurements highlight the efficient and simple method for perovskite devices.Intensively red luminescence non-rare-earth phosphor Sr4Al14O25:Mn4+,0.5%Mg has been encapsulated in poly(methyl, methacrylate) (PMMA) as luminescent down-shifting coatings for NiO/CH3NH3Pbl3/PCBM perovskite devices, incorporating light-management, UV-protection, and waterproof capabilities. The combined device system gives a 10% relative increase in power conversion efficiency as compared with the control devices. Device stability test in ambient air reveals the excellent UV protecting effect of the new coating on perovskite solar cells, which shows an improved stability under prolonged illumination and retains more than 50% of its initial efficiency, whereas device without the phosphor layer degraded to ?25% of its initial value. The encapsulated perovskite devices with this luminescent/resin coating combine the UV down-shifting conversion enhancement and superior stability, which arises from UV-protecting and water-resistant properties. Details of the UV accelerated CH3NH3PbI3 degradation process are investigated.