Accelerated depletion of fossil fuel, energy demands, and pollution force us to choose renewable and eco-friendly energy resources. Solar cells are considered as an efficient replacement for fossil fuel. In the family of solar cells, silicon-based solar cells and perovskite solar cells (PSC) have displayed significant power conversion efficiency (PCE). Perovskites have been investigated extensively over the past two decades, due to their advantageous properties, such as high absorption coefficient, efficient carrier mobility, long charge diffusion length, and direct bandgap. These features make PSC a prospective candidate to replace silicon in solar cells. By 2018, PSC achieved an encouraging PCE of 23.3%. However, low stability and toxicity have retarded the commercialization of PSC. With the aim of assisting junior researchers, we consider the latest achievements in this domain and review the field from a stability and performance perspective. We emphasize recent developments and methodologies to overcome drawbacks concerning stability and toxicity.

Vertically aligned zinc oxide (ZnO) nanostructures (NS) have been fabricated without any catalyst on Si (100) and sapphire (0002) substrates using high-pressure-assisted pulsed laser deposition technique. It has been observed that the substrate plays a crucial role in deciding the morphology and optical quality of the nanostructures, wherein ZnO NS on Si substrate exhibit better luminescence characteristics as compared to those grown on sapphire substrate. Gallium nitride (GaN) layers are grown using a customized laser molecular beam epitaxy system and the effect of an intermediate layer in the form of vertically aligned ZnO NS is analyzed. A comparative study is performed with GaN layers grown on ZnO NS-coated Si, bare Si, and bare sapphire substrate. The structural and room temperature photoluminescence properties of the GaN layer significantly improve when grown on ZnO-NS/Si substrates as compared to bare sapphire and Si substrate.

We perform a device modeling study on an inverted-structure perovskite solar cell (PSC) with ZnO as an electron transport layer and NiO_x as a hole transport layer (HTL). The influence of several parameters on solar cell performance is explored. The simulation indicates that the optimal values for the absorber thickness and the HTL thickness are 600 and 30 nm, respectively. Meanwhile, doping concentrations of NiO_x and ZnO can significantly affect the device performance. Hole mobility of HTL larger than 0.1  cm²  /  V  ·  s is necessary for the effective hole transporting to the front contact. In addition, a front contact work function higher than 4.8 eV is more suitable for the inverted-structure PSCs. By optimizing these parameters, high-performance inverted-structure PSC with the efficiency of 21.28% is achieved. These research results are conducive to device design and fabrication of inverted PSCs.

Theoretical modeling of the incidence angle dependence is important for the performance evaluation of solar cells especially when they employ structural photonics that enhance their aesthetics for building-integrated photovoltaic applications. We present an optical model based on transfer matrix method, which is tailored for the analysis of the angular optical characteristics of dye-sensitized solar cells (DSSC) that incorporate a porous one-dimensional photonic-crystal (1DPC) back reflector. We provide complete mathematical description of the angular optics and electromagnetic energetics of DSSC, including solutions that avoid numerical instabilities in the case of thick, strongly light-absorbing layers. The model showed excellent quantitative agreement with angle-dependent spectral transmittance measurements recorded from complete DSSCs, allowing detailed analysis of the light harvesting enhancement by the dye provided by back-reflection of light from the 1DPC. Determining the ratio of the device transmittance measured with and without a 1DPC is proposed as a simple and practical way to determine the internal reflectance of the 1DPC embedded in the device structure. The reported model provides an accurate description of the coherent angular optics of DSSCs, applicable for situations where light scattering in the device structure can be neglected.

A number of image microscopies have been applied to films of π-conjugated polymers and their fullerene blends used in photovoltaic applications; however, they seldom are able to map the polymer/fullerene grain interfaces and detect microscopic defects in the blend films. We have conducted multiphoton microscopy using a 65-fs mode-locked laser at 1.56  μm for spectroscopy and mapping of films of two prototype π-conjugated polymers, namely MEH-PPV and P3HT combined with their blends of PCBM fullerene molecules. The pristine polymer films have shown third harmonic generation and three-photon photoluminescence emission bands that are used for mapping the film topography with micrometer spatial resolution. Since the nonlinear photoluminescence band of the photogenerated charge transfer excitons (CTE) at the polymer/fullerene interfaces in films of polymer/fullerene blends is substantially redshifted compared to that of the excitons in pristine polymers, we could readily map the polymer/fullerene grain interfaces using the nonlinear CTE photoluminescence emission. From the multiphoton imaging of the polymer/fullerene films, we show that the polymer super-grains in MEH-PPV/PCBM are substantially larger than those in P3HT/PCBM, which may be detrimental to charge transport and, in turn, to photovoltaic applications, in agreement with smaller power conversion efficiencies obtained for solar cells based on the former blend. In addition, we also found second harmonic generation emission bands in the MEH-PPV/PCBM blend that result from micron-size embedded defects that do not possess inversion symmetry that forms during the film deposition process at ambient conditions. Multiphoton microscopy and spectroscopy are valuable additions to the tools of organic semiconductor films and devices for investigating the properties and growth of polymer/fullerene blends used for photovoltaic applications with micron spatial resolution.

We demonstrate an effective approach to enhancing the performance of III-nitride-based photoelectrode by utilization of hot electrons generated from localized surface plasmons (LSPs). The device designed as a TiO₂  /  Au  /  InGaN sandwich structure is fabricated by cladding Au nanodroplets with a thin TiO₂ layer to provide a large interfacial layer, which is beneficial for the hot electron collection efficiency by electron reflection via an additional energy barrier. The applied bias photo-to-current efficiency is enhanced by up to four times due to the contribution of hot electrons generated from the absorbed light with wavelengths >470  nm, corresponding to photon energies below the band gap of InGaN (2.67 eV) recognized from incident photon-to-current efficiency spectrum. The LSPs of our photoelectrodes also exhibit a suppressed size-dependence on the metal nanodroplets, feasible for mass production.

We report a one-dimensional porous intergrowth structure consisting of amorphous α-Fe₂O₃ and akaganeite (β-FeOOH). The homojunction, which features an intimate interface as well as a clean surface, facilitates charge separation and thus improves the photocatalytic O₂ evolution activity. The success of the synthesis relies on a phase-transition process that involves the dehydration of β-FeOOH tetragonal nanorods (5.02 nm in average diameter and 25.51 nm in length, respectively). We find that the selective calcination temperature is crucial for retaining the rod shape, creating proper surface pores and intermediate phase segregations. If the temperature is too high (300°C), only crystallized α-Fe₂O₃ can be obtained. At a depressed temperature, intermediate amorphous α-Fe₂O₃, instead of the crystallized counterpart, largely emerges in situ, leading to the formation of amorphous α-Fe₂O₃  /  β-FeOOH intergrowth homojunctions. This preferential growth together with a type-II band alignment favors vertical interfacial charge transfer between the two components. Our results show that amorphous α-Fe₂O₃  /  β-FeOOH porous nanorods prepared at 200°C present a profound photocatalytic activity toward water oxidation. The rate of oxygen evolution reaches 90  μmoL h^−  1 g^−  1 under visible light irradiation without the addition of a cocatalyst. We believe the method can be extended for the design of other intergrowth junction structures for efficient photocatalysis.

We explore the visual appearance of microscale silver grids for use in solar windows. The distortion of view is investigated by ray optical computations and experiments. We find that the visual appearance strongly depends on the geometric properties of the microcontacts (i.e., shape, aspect ratio, and periodicity) as well as on the viewing angle. From a perpendicular view, glass substrates appear marginally darker with microcontacts. In the case of effectively transparent triangular cross-section microcontacts, observation of scenes under a steep angle with respect to the substrate leads to the appearance of “ghost images.” Scenes are projected through redirection of rays by triangular cross-section microcontacts which can be tuned by adjusting aspect ratio and periodicity.

Photovoltaic thermal systems working with different nanofluids and using deionized water as base fluid were investigated experimentally. The performance of nanofluids with 1% volume fraction was compared, including carbon, CuO, Al₂O₃, SiO₂, and graphite nanofluids. It was observed that the SiO₂ nanofluid shows the best solar absorbing property among them. It contributes to the best performance of photovoltaic thermal systems with an overall power of 2.609 W, followed by the systems using carbon, graphite, Al₂O₃, CuO nanofluid, respectively. An experiment for a separated PV system was conducted under the same conditions with an obtained electric power of 0.175 W, which is significantly lower than heat absorbing power and higher than that of a PV subsystem. We indicate that the PV system working with nanofluids can improve the overall outcomes in solar power generation.

We present here a tracking error compensation concept in solar-pumped lasers, by pumping two thin laser rods simultaneously, each rod by half of the solar collector area instead of the mostly used scheme with one thick rod pumped by a full solar collector area. A semicylindrical fused silica lens allows an efficient focusing of the concentrated solar power from the focal spot of the parabolic mirror into the two thin laser rods mounted within two compound parabolic concentrator-semicylindrical pump cavities. The multimode solar laser output power, the threshold pump power, and the slope efficiency of a single-rod scheme, a dual-rod scheme with two laser beams, and a dual-rod scheme with one laser beam are calculated both numerically and analytically, revealing a clear advantage of the dual-rod one laser beam scheme in terms of solar laser output power and threshold pump power. A large improvement in tracking error compensation capacity is numerically attained with this new approach, leading to 2.57 and 3.00 times enhancement in tracking error width at 10% laser power loss in ΔY (altitude) and ΔX (azimuth) errors, respectively, as compared to the most efficient end-side-pumped scheme by the same collection area.