Among various solar cell architectures, dye-sensitized solar cells (DSSCs) and perovskite solar cells have demonstrated the capability of being bifacial as both can be fabricated on conducting glass electrodes. In both cells, TiO₂ plays a key role in the optoelectronic properties of the cell. Various studies have reported a range of recipes and deposition techniques for TiO₂ thin films. Such variety introduces some uncertainties into the optical properties of the prepared films as well as in the process repeatability. Here, we utilized machine learning methods to correlate the film porosity to the film refractive index, making it capable of studying the impact of varying the fabrication and deposition techniques. Image postprocessing for scanning electron microscope measurements was utilized to estimate the film porosity, and the refractive index was calculated from the T–λ spectra. Four sets of samples with complete bifacial DSSCs were fabricated and characterized. They recorded a maximum current of 23.42 mA. They were fabricated using carboxymethyl cellulose-based suspension and deposited via the spin-coating sol-gel method. The fabricated cells showed an overall conversion efficiency of 7.9% under optical injection of the AM1.5G spectrum from the front side and LED indoor lighting from the counter electrode.

Epitaxially grown quantum well and quantum dot solar cells suffer from weak light absorption, strongly limiting their performance. Light trapping based on optical resonances is particularly relevant for such devices to increase light absorption and thereby current generation. Compared to homogeneous media, the position of the quantum layers within the device is an additional parameter that can strongly influence resonant absorption. However, this effect has so far received little attention from the photovoltaic community. We develop a theoretical framework to evaluate and optimize resonant light absorption in a thin slab with multiple quantum layers. Using numerical simulations, we show that the position of the layers can make the difference between strong absorption enhancement and completely suppressed absorption, and that an optimal position leads to a resonant absorption enhancement two times larger than average. We confirm these results experimentally by measuring the absorption enhancement from photoluminescence spectra in InAs/GaAs quantum dot samples. Overall, this work provides an additional degree of freedom to substantially improve absorption, encouraging the development of quantum wells and quantum dots-based devices such as intermediate-band solar cells.

Hot carrier solar cells (HCSCs) were first proposed many decades ago. Over the intervening years, there has been a continuing quest to create these cells that hold promise to shatter the Shockley–Queisser efficiency limit on single-junction solar cells. While there have been many positive and suggestive results in recent years, there remains no true operational HCSC. There are perhaps many reasons for this state. Here, many of the requirements for achieving such an HCSC will be discussed and some approaches will be modernized in terms of their science. Valley photovoltaics, in which carriers are transferred to higher-lying valleys of the conduction band will be described and the recent progress is discussed.

The optical properties of Λ-graded indium gallium nitride (InGaN) solar cells are studied. Graded InGaN well structures with the indium composition increasing to x_max and then decreasing in a Λ-shaped pattern have been designed. Through polarization doping, this naturally creates alternating p- and n-type regions. Separate structures are designed by varying the indium alloy profile from GaN to maximum indium concentrations ranging from 20% to 90%, while maintaining a constant overall structure thickness of 100 nm. The solar cell parameters under fully strained and relaxed conditions are considered. The results show that a maximum efficiency of ≅5.5  %   under fully strained condition occurs for x_max  =  60  %  . Solar cell efficiency under relaxed conditions increases to a maximum of 8.3% for x_max  =  90  %  . Vegard’s law predicts the bandgap under relaxed conditions, whereas a Vegard-like law is empirically determined from the output of nextnano™ for varying indium compositions to calculate the solar cell parameters under strain.

We examine the potential of a multijunction spectrum-splitting photovoltaic (PV) solar energy system with perovskite PV cells. Spectrum splitting allows combinations of different energy band gap PV cells that are laterally separated and avoids the complications of fabricating tandem stack architectures. Volume holographic optical elements have been shown to be effective for the spectrum-splitting operation and can be incorporated into compact module packages. However, one of the remaining issues for spectrum splitting systems is the availability of low-cost wide band gap and intermediate band gap cells that are required for realizing high overall conversion efficiency. Perovskite PV cells have been fabricated with a wide range of band gap energies that potentially satisfy the requirements for multijunction spectrum-splitting systems. A spectrum-splitting system is evaluated for a combination of perovskite PV cells with energy band gaps of 2.30, 1.63, and 1.25 eV and with conversion efficiencies of 10.4%, 21.6%, and 20.4%, respectively, which have been demonstrated experimentally in the literature. First, the design of a cascaded volume holographic lens for spectral separation in three spectral bands is presented. Second, a rigorous coupled wave model is developed for computing the diffraction efficiency of a cascaded hologram. The model accounts for cross-coupling between higher diffraction orders in the upper and lower holograms, which previous models have not accounted for but is included here with the experimental verification. Lastly, the optical losses in the system are analyzed and the hypothetical power conversion efficiency is calculated to be 26.7%.

Concentrated photovoltaic (PV) technology represents a growing market in the field of terrestrial solar energy production. As the demand for renewable energy technologies increases, further importance is placed on the modeling, design, and simulation of these systems. Given the cultural shift toward energy awareness and conservation, several concentrated PV systems have been installed across the world. This research presents a new model for carrier concentration within a solar cell. The goal of this innovation is to facilitate the determination of the steady-state operating temperature as a function of the concentration factor for the optical part of the concentrated PV system, to calculate the optimum concentration that maximizes power output and efficiency. This model will be shown to produce a more realistic estimate of the current through a solar cell, which will enable further research into dynamic thermal modeling.

Susceptibility to environmental factors, such as moisture, humidity, oxygen, heat, and ultraviolet (UV) light (photoinstability), has affected perovskite solar cell (PSC) stability in practical applications. To overcome the instability and performance degradation due to oxygen, humidity, and moisture, different strategies and encapsulation schemes have been proposed, and promising results have been obtained. However, photostability remains a major hurdle because UV light is an inherent part of the standard incident spectrum of PSCs. To prevent photoinstability and increase quantum energy harvesting levels, cadmium chalcogenide (CC) photoluminescent (PL) filters for downconverting the UV part of the incident spectra obtained for PSCs are proposed in this work. The concept was illustrated by matching 500-nm-thick CC-PL filters to the front glass of a PSC to form a CC-PL/glass/indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)/perovskite/Ag structure. Cadmium sulfide (CdS), cadmium selenide, and cadmium telluride were taken as the CC materials. Practical measurements confirmed that the PSC with the CdS-PL filter can maintain 92% of its initial value under continuous light soaking for more than 100 h. Furthermore, this PSC exhibited the best improvement in power conversion efficiency.

A physics-based analytical model is important to understand the working mechanism through process parameters of any innovative material heterostructure. We present an analytical model to calculate the power conversion efficiency of solar cells based on graphene and III-V direct bandgap semiconductors. The model is comprehensively developed by incorporating several current densities obtained from both the generation and recombination processes. Moreover, to obtain a highly efficient Schottky junction solar cell, we propose an optimized structure of graphene/GaAs with lattice-matched passivation and carrier selective layers. The structure has the advantage of surface passivation and photon recycling that reduces interface recombination and ensures more electron–hole pair generation, respectively. It exhibits a theoretical efficiency of >18  %   from the analytical model simulation which is later verified by numerical simulation using SCAPS 1D software. The analytical model will provide not only a better understanding of the solar cells’ operation but also a comparative study among them to achieve better efficiency in the future. In addition, the enhanced efficiency of the proposed structure will encourage further research in this field of study.

The efficiency of solar-pumped lasers (SPLs) is limited when the length of the laser medium is unsuitable. This is because superfluous regions in the laser medium introduce losses and contribute slightly to the stimulation of radiation in the laser resonator. Before designing an SPL, an appropriate length of laser medium is critical. We present a method to calculate the optimal length of the gain medium in SPLs by exploring the relationship between the absorbed solar power and material loss for different laser medium lengths. Thus, the lengths of Nd:YAG crystals with diameters of 3 to 6 mm were optimized, and the output characteristics were calculated numerically. The maximum collection efficiency (CE) (40.1  W  /  m²) was obtained for the 5.5-mm diameter Nd:YAG crystal rod of length 21.1 mm, which was 1.7  W  /  m² higher than the previous numerical record. The optimal length of the 6-mm diameter Nd:YAG crystal rod was found to be 21.9 mm. For a laser rod of this length, a CE of 36.3  W  /  m² is expected. This value is 1.13 times greater than the existing experimental record for the Nd:YAG crystal of the same diameter, which highlights the importance of optimizing the length of the laser rod.