The editorial introduces the JPE Special Section on Novel Photovoltaic Device Architectures.

JPE Editor-in-Chief Sean Shaheen interviewed JPE authors Maxime Giteau, Samy Almosni, and Daniel Suchet about the research presented in their recently published article, “Hot-carrier multijunction solar cells: sensitivity and resilience to nonidealities” (doi https://doi.org/10.1117/1.JPE.12.032208).

Significant progress in the development of nonreciprocal optical components with broken Kirchhoff symmetry paves the way for increasing the photovoltaic (PV) conversion efficiency beyond the Shockley–Queisser limit due to reuse of emitted photons. Recent papers have analyzed the PV converter with several or an infinite number of multijunction cells, in which the cells are coupled via nonreciprocal filters (optical diodes) in such a way that the light emitted by one cell is absorbed by another cell. We proposed and investigated a single cell converter with nonreciprocal external photon recycling, which provided reabsorption and reuse of the emitting light by the same cell. We considered properties of photons in the sunbeam in terms of ergodicity, disorder, energy availability, information entropy, and coherence, and established fundamental limitations imposed by endoreversible thermodynamics on conversion efficiency at maximal power output. Our results show that the nonreciprocal converter with an ideal multijunction cell can approach the Carnot efficiency, whereas operating exactly at the Carnot limit requires an infinite number of photon recycling processes. This requirement resolves the famous thermodynamic paradox of the optical diode because any small dissipation in the cell or optical system enhanced by infinite recycling will stabilize the converter operation below the Carnot limit. We generalized endoreversible thermodynamics to photonic distributions with nonzero chemical potential and derived the limiting efficiency of the nonreciprocal single-junction PV converter. The performance of this converter with available GaAs solar cells was evaluated.

The resilience against non-idealities of hot-carrier multijunction solar cells (HCMJSCs) is assessed and compared with two references, namely a multijunction solar cell (MJSC) and a hot carrier solar cell (HCSC). We investigate the impact on the efficiency of three deviations from the ideal case: nonoptimal design, internal limitations, and nonstandard operation conditions. We show that the HCMJSC maintains a high efficiency even when materials with nonoptimal bandgaps are considered, broadening the range of candidate materials for its implementation. We also show that the requirement for hot carriers’ thermalization is much less stringent than with the standard HCSC architecture, allowing to surpass the best MJSC efficiency with currently achievable thermalization coefficients. Finally, we estimate the influence of nonstandard illumination by varying the AM spectrum and estimate numerically the yearly averaged efficiency of devices installed in two different locations. Preliminary results on temperature dependence are also presented.

Type-II multiple quantum well superlattices based on InAs/AlAsSb are investigated for ground- and excited-state charge carrier transport and excited-state charge carrier dynamics. It is found that ground-state transport matches well to impurity and optical phonon interactions, while the excited-state transport shows increased terahertz photoconductivity for the correct excitation conditions that have previously been linked to a metastability in the early time response after photoexcitation. This regime also shows a reduction in carrier mobility, which is also expected to be due to ambipolar diffusion and increased carrier–carrier scattering. Overall, carrier excited-state dynamics confirm the metastability in early time response and are related to strong Auger scattering. For increased excitation intensities, the Auger-scattering rate increases to obtain a lower carrier density more rapidly. The result is a stronger scattering of carriers energetically deeper into their respective bands, where they exhibit a much slower carrier recombination rate and can maintain their relative temperature as a result of a phonon bottleneck that forces reabsorption of optical phonons. In addition to a previously reported phonon bottleneck, the carrier dynamics offer potential pathways to stabilize hot carriers with further bandgap engineering.

The unique electronic features of highly mismatched alloys such as III-V GaNAs are suitable for the intermediate band solar cell (IBSC) application, in which an intermediate band (IB) acts as a stepping stone to generate additional photocarriers across the host semiconductor bandgap through sequential two-step below-bandgap photon absorption (TSPA). However, the collection of photocarriers in a realistic GaNAs IBSC is much lower and often accompanies S-shape kink features in the current–voltage (J–V) curves under illumination for which a coherent picture is lacking. Based on the solar cell characterization of GaNAs IBSC devices grown with and without barriers, with and without antimony, and with and without indium using molecular beam epitaxy, and also with the photocarrier collection analysis using equivalent circuit models, it was identified that the TSPA and the S-shape J–V of this system depend on two critical factors: (1) high carrier recombination currents (I0CI) across the GaNAs sub-gap between the conduction- and intermediate bands (EgCI) and (2) the counterdiode effect of the AlGaAs IB electron barrier. Dramatic improvements in the S-shape J–V feature of the solar cell characteristics were achieved when lattice-strain was compensated in GaInNAsSb epitaxial layers.

Recently, all-inorganic double perovskite, lead-free absorber-based perovskite solar cells (PSCs) have been an active area of research. Due to its narrow bandgap and wide and high absorption, Cs₂PtI₆-based PSCs have generated wide interest. In this work, a comprehensive study of a Cs₂PtI₆-based PSC using solar cell capacitance simulator (SCAPS) one-dimensional is conducted. The simulation result is validated by comparing it with experimentally reported Cs₂PtI₆-based PSCs. To design a highly efficient, commercially feasible PSC, the variation in the performance of the PSC with six different electron transport layers (ETLs), ten-hole transport layers (HTLs), and nine metal contacts is investigated by simulation. Among the tried configurations, FTO / ZnO / Cs₂PtI₆ / MoO₃ / Cu yielded the highest power conversion efficiency (PCE). The effect of varying the parameters of thickness, defect density, and doping concentration of the absorber layer; thickness, and doping concentration of the transport layers; and defect density of the interface layers on the performance of the device is investigated. The optimized device configuration yields an open-circuit voltage (Voc) of 1.3856 V, short-circuit current density (Jsc) of 16.107 mA / cm², fill factor (FF) of 75.54%, and PCE of 16.85%. When the simulation is done with different back metal contacts, carbon yielded encouraging results with a Voc of 1.4105 V, Jsc of 16.112 mA / cm², FF of 90.01%, and PCE of 20.45%.

We studied possible techniques for increasing the power-to-power conversion efficiency of the Ce:Nd:YAG solar laser using a simulation model developed with the Monte-Carlo photon tracing method framework. It is suggested that the multi-passage of photons through a medium can enhance the absorption probability. The effectiveness of the multi-pass scheme is experimentally investigated. The application of the multi-pass pumping scheme for Ce:Nd:YAG solar lasers is demonstrated. It is shown that the pumping efficiency in the Ce:Nd:YAG solar laser with the multi-pass pumping cavity is increased by 20%, paving the way for higher power-to-power conversion efficiency.

Here, we studied the influence of pre- and post-thermal annealing on the performance of polymer:fullerene bulk heterojunction solar cells using the conventional architecture, comprising a conjugated polymer, namely, poly(3-hexylthiophene-2,5-diyl) (P3HT) and a fullerene derivative [6,6]-phenyl-C60-butyric acid methyl ester (PC₆₀BM) as a photoactive layer. The non-annealed active layer device exhibited a power conversion efficiency of <1 % , which was significantly lower than the pre- and post-annealed devices. To investigate the impact of pre- and post thermal annealing on the natural morphological state of the polymer, regiorandom (P3HT-I) and regioregular (P3HT-II) type P3HT were compared in photoactive layers. In general, P3HT-I is amorphous, whereas P3HT-II is semi-crystalline. Changes in solar cell performance were associated with changes in carrier extraction efficiencies influenced by the annealing conditions. The charge photogeneration processes were investigated using spectroscopic techniques, including electroluminescence, steady-state, and time-resolved photoluminescence spectroscopy. Finally, to explore the morphological changes upon annealing, atomic force microscopy and electroluminescence imaging measurements were performed on films and solar cells, respectively.

Cotton rope has good water transport performance and plasticity. An efficient three-dimensional evaporator for solar evaporation was prepared by winding the cotton rope into different shapes and covering its surface with carbon black (CB). The light absorption of the evaporator coated with CB was significantly improved, and the average absorptance was 95.8% over the solar spectrum. Using a one-dimensional channel for water supply, the evaporator and bulk water were separated, and thermal localization was realized without thermal insulation materials. The influence of the evaporator shape on evaporation performance was analyzed. Under the same conditions, the evaporation rate of funnel-shaped evaporator was the highest, reaching 1.3033 kg / m² h. The multiple reflection of light in the funnel-shaped evaporator promoted the capture and absorption of incident light. For the evaporator with a reflector placed below, the evaporation rates of funnel-shaped, plane-shaped, and umbrella-shaped evaporators increased by 2.3%, 1.67%, and 0.814%, respectively. In addition, the evaporator has a self-cleaning function. The salt deposited on the surface can be redissolved and leaves the evaporator with water. An efficient solar evaporator was designed in a simple and economical way. Its self-cleaning function is especially suitable for seawater desalination.

A four-rod/four-TEM₀₀-mode beam off-axis parabolic mirror solar pumping concept is proposed. Four off-axis parabolic mirrors with 10 m² total collection area were used as the primary solar concentrators to pump four 3.1-mm diameter, 84-mm length neodymium-doped yttrium aluminum garnet (Nd:YAG) rods within four 2V-shaped pump cavities through four secondary fused-silica aspheric concentrators and four rectangular fused-silica light guides, ensuring a good absorbed pump power distribution within each rod and avoiding the serious thermal lensing and thermal stress issues associated with classical single large rod solar lasers. The laser design parameters were optimized using ZEMAX^© and LASer Cavity Analysis and Design (LASCAD^©) analysis software to maximize the TEM₀₀-mode laser power. 155.29-W TEM₀₀-mode total laser power was numerically calculated, corresponding to 15.5 W / m² solar laser collection efficiency and 1.72% solar-to-TEM₀₀-mode laser conversion efficiency, respectively. This result represents an improvement of nearly 2 and 1.24 times, in solar laser collection efficiency and solar-to-TEM₀₀-mode laser conversion efficiency, respectively, as compared with the previous experimental records of the TEM₀₀-mode solar laser pumped through the parabolic mirror primary concentrator. It provides also a 1.14 and 1.19 times improvement, as compared to the previous numerical record of the TEM₀₀-mode solar laser pumped by the Fresnel lens primary solar concentrator.