Progress in Photovoltaics最新文献

This work examines the feasibility and performance impact of replacing the usual molybdenum back contact with indium-free transparent conductive oxides (TCOs) like fluorine-doped tin oxide (SnO₂:F) and aluminum-doped zinc oxide (ZnO:Al) for ultra-thin Cu (In,Ga)Se₂ (CIGS) solar cells (250–450 nm). Motivated by indium scarcity and cost reduction, these TCOs are evaluated for their figure of merit, stability under Se atmosphere, Na diffusion permeability, and band alignment with CIGS absorbers. Using simulations, prototype fabrication, and comprehensive characterizations, the compatibility of these TCOs with CIGS absorbers is assessed. Solar cells with thicknesses of 450 and 250 nm are fabricated. Their performance was compared under both rear and front illumination, as well as with the use of reflectors. A record efficiency of 8.6% with front illumination is achieved for a 250-nm CIGS absorber using a gold back reflector with SnO₂:F, single-step CIGS deposition, and no heavy alkalines doping. The best rear-illuminated efficiencies are obtained with ZnO:Al back contacts, reaching 6% for a 250-nm CIGS, with only a 9% loss in J_sc compared to front illumination, confirming a lower surface recombination rate at the ZnO:Al/CIGS interface compared to Mo/CIGS or SnO₂:F/CIGS interfaces.

Optimal bandgap combination to deliberately split the solar spectra is the key to high efficiency multijunction solar cell design. III-V Multijunction solar cells with more than four junctions require an inverted top subcell with specific bandgap wider than 2.1 eV to absorb the short-wavelength photons (< 600 nm) effectively. (Al_xGa_1-x)_0.5In_0.5P alloy lattice-matched to GaAs substrate, with x ≥ 0.31, is usually preferred. However, it has been a challenge to achieve high performance inverted 2.1 eV AlGaInP homojunction solar cells for the severe decrease of short-wavelength (especially for wavelength < 450 nm) quantum efficiency. Thus, until now, a compromise structure replacing the n-type emitter with a narrow bandgap material (for instance, 1.91 eV GaInP), which is called the heterojunction solar cell, is widely employed. However, this structure would decrease the open-voltage for increasing energy loss of short-wavelength photons and limit the multijunction device efficiency. Here, we investigate the underlying mechanisms besides those commonly known results and present arguments that two new mechanisms should be attributed to the degradation of short-wavelength quantum efficiency: (1) bulk AlGaInP quality degradation resulting from the underneath AlInP window surface morphology and (2) additional optical absorption of the intermediate layers formed by III-V atom intermixing. Based on these findings, an interface Induced lifetime decrease model, and an intermixing layer model are introduced into the numerical simulations to time-resolved photoluminescence and internal quantum efficiency, achieving nice agreement between measured and modelled data with reasonable input parameters. Consequently, two strategies, 1) thermal treatment for AlInP layers and 2) minor compressive strain in P—containing materials, are suggested not only for the inverted 2.1 eV AlGaInP homojunction solar cells but also for the inverted 2.1 eV/1.7 eV/1.4 eV triple-junction solar cell. The subcells with these two strategies show higher quantum efficiency than the normal ones despite the bandgaps changing from 2.12 eV to 2.15 eV (e.g., IQE@400 nm increases from 69% to 76%). Meanwhile, the fill factor of inverted triple junction solar cells is slightly enhanced from 0.85 to 0.87. This improved triple junction solar cell is bonded with a 1.1 eV/0.83 eV dual-junction solar cell to form a five-junction solar cell, achieving an outstanding one-sun AM0 efficiency of 36.06% (Voc:4.904 V, Jsc:11.51 mA/cm², FF:0.8645). The efficiency gain, compared with those previously reported, is attributed to the thermalization loss reduction of short-wavelength photons for using a high spectral response 2.15 eV homojunction top cell.

Integrating carbon quantum dots (CQDs) into the CdTe photovoltaic (PV) cell is anticipated to significantly enhance its power generation performance. This improvement could lead to reduced building energy consumption and lower carbon emissions, particularly when applied to CdTe PV façades widely in modern architecture. In this study, silicon-functionalized carbon quantum dots (Si-CQDs) were synthesized using a one-step hydrothermal method, and their optical properties, morphological structure, and surface composition were thoroughly characterized. When the reaction was conducted at 180°C and maintained at room temperature for 10 h, the Si-CQDs achieved a high quantum yield of 86.67% for blue light emission with the addition of 6.6 mL of N-[3-(Trimethoxysilyl)propyl]ethylenediamine (KH-792). The Si-CQDs exhibited stable fluorescence over a 2-month storage period and 48 h of ultraviolet (UV) irradiation. Subsequently, Si-CQDs@PVA thin films were fabricated using a scraping coating method to investigate their effects as a luminescent downshifting (LDS) layer on the performance of CdTe PV cells. It was found that with the application of a 1.5-mL thin-film slurry, the short-circuit current density (J_sc) increased from 0.82 to 0.84 mA·cm⁻², and the maximum power output (P_max) increased from 0.192 to 0.201 W, corresponding to a 4.76% enhancement in power generation efficiency.

PL-based external radiative efficiency (ERE) and implied open-circuit voltage (iV_OC) metrics were introduced for thin-film solar absorbers to better understand the voltage deficit and diagnose losses in solar cells. Traditionally, elevated ERE and iV_OC measurements are associated with diminished recombination within the solar device, a rationale heavily reliant on the assumption of a uniform bandgap and high carrier mobilities in the absorber. Recently, very low mobilities in CdSeTe absorbers (< 1 cm²/(V·s)) were measured using the light-induced transient grading technique. In this study, we use a detailed numerical model of iV_OC to investigate the possible reasons of elevated iV_OC in realistic CdSeTe absorbers with a graded Se profile. In particular, we examine how the bandgap nonuniformity and the reduced hole mobility in graded CdSeTe absorbers affect iV_OC measurements. We show that high iV_OC may result from inflated quasi-Fermi level splitting in the high-Se region in the front part of a CdSeTe absorber with slow hole transport. We reproduce the experimentally reported 360 mV increase in iV_OC–V_OC gap with reduced doping using a model with sub-1 cm²/(V·s) hole mobility in the high-Se region. Based on our results, we conclude that the iV_OC metric (or ERE metric) should not be used as a sole metric of CdSeTe absorber quality. We discuss possible ways to extract useful information from the iV_OC–V_OC gap by supplementing the front-side illumination measurements with back-side illumination measurements.

Potential-induced degradation (PID) presents a significant challenge to the long-term reliability of perovskite solar cells (PSCs) in commercial applications. Research on PID in PSCs is still in its early stages, and the polarization-type PID (PID-p) remains poorly understood. In this study, we used advanced microscopic techniques to investigate the underlying mechanisms of PID-p in PSCs. After 100 h of PID stress, the devices experienced severe performance loss, with efficiency reduced to 20.9% of its initial value. This degradation was primarily driven by a decrease in short-circuit current and fill factor, while the open-circuit voltage remained relatively stable. Our findings reveal that the accumulation of sodium ions at the glass/film interface triggers the formation of an electron inversion layer at the perovskite's bottom, leading to performance decline. Electrical and mechanical characterizations further confirm changes in material properties, particularly at the hole transport layer/perovskite interface, contributing to the degradation.

In photovoltaic applications, the rear surface morphology of tunnel oxide passivated contact (TOPCon) solar cells plays a critical role in their performance. However, traditional textured and polished surface morphologies both have limitations. This study introduces a hybrid nano-pyramid/polish morphology, combining a nano-pyramid structure on a polished surface. This new design aims to capitalize on the advantages of both textured and polished surfaces, achieving an optimal balance for TOPCon performance. The balance is achieved through an additional chemical solution treatment process. When applied to TOPCon solar cells, the hybrid structure outperforms both secondary-textured and polished morphologies in terms of optical absorption, passivation, and contact performance. The nano-pyramid/polish hybrid achieves a superior balance between light trapping, passivation, and contact quality. Furthermore, the study investigates the impact of rear surface morphology on film blistering, revealing that rougher surfaces are less prone to blistering. This is likely due to more favorable stress distribution in the SiO_x/poly-Si stack, enhancing mechanical stability. These findings demonstrate the compatibility of the hybrid nano-pyramid/polish morphology with TOPCon solar cells, offering a promising pathway to enhance efficiency. The insights gained may also benefit the development of other high-performance solar cell technologies, such as heterojunction (HJT) and silicon/perovskite tandem solar cells, advancing industrial photovoltaic applications.