Although metallic aluminum (Al) is an attractive back electrode material for cadmium telluride (CdTe) solar cells due to its low cost and suitability for large-area deposition, its low work function has hindered widespread application. To overcome this challenge, we designed and implemented a molybdenum-chromium (Mo/Cr) interfacial modification layer. A comprehensive comparative analysis was carried out to evaluate the electrical characteristics, interfacial transport properties, and device performance of the Al, Mo/Cr-modified Al and Au electrodes. The results reveal that the Mo/Cr interfacial modification layer effectively improves Al-electrode interfacial transport properties and conductivity and also blocks the diffusion of Al atoms. The optimized device with a Mo/Cr-modified Al electrode achieved a champion efficiency of 15.68%, closely approaching 15.88% of the expensive, high-work-function gold (Au) reference and significantly surpassing 13.83% of the Al electrode. Furthermore, it exhibited excellent mechanical adhesion and wear resistance, with a critical load of 0.62 mN, substantially higher than the 0.45 and 0.42 mN for the Al and Au electrodes, respectively. This electrode architecture offers a low-cost, highly durable, and high-performance alternative to noble-metal contacts, showing great potential for facilitating the large-scale commercialization of thin-film photovoltaic technology.

Introducing a 2D perovskite layer on the surface of 3D perovskite has been broadly recognized as an effective strategy to enhance the performance of perovskite solar cells (PSCs). However, the mechanism governing the 2D phase formation remains uncertain. In this work, the phase transitions of 2D perovskite during spin-coating and annealing processes has been investigated. Our findings reveal a dimensional phase shift from low to high n-value 2D phases, driven by the release of organic cations during annealing. Additionally, the spin-coating process exhibited concentration-dependent behavior, where higher n-octylamine hydrobromide (OABr) concentrations predominantly formed n = 1 phases. These observations highlight the complexity of the 2D phase composition at the 2D/3D interface. The coexistence of various 2D phases significantly influences device performance, as a conflict between n = 1 and n ≥ 2 phases was identified. Through forming a well-balanced proportion of different 2D phases, we achieved a wide-bandgap perovskite solar cell with a significantly improved power conversion efficiency of 19.29%. This work suggests the critical roles of phase dynamics and n-value distribution in optimizing 2D/3D interfaces for advancing high-performance wide-bandgap PSCs.

Abstract Against the global demand for renewable and sustainable clean energy, perovskite solar cells (PSCs) have shown great potential as a next-generation photovoltaic technology, owing to their high photoelectric conversion efficiency (PCE) and low-cost potential. Although the highest PCE of PSCs has exceeded 27%, poor stability and severe nonradiative recombination loss still hinder their further development. PSCs contain several critical interfaces, including the electron transport layer (ETL)/perovskite, hole transport layer (HTL)/perovskite, and charge transport layer (CTL)/electrode, which strongly influence carrier dynamics and dominate device efficiency and stability. Interface engineering has attracted extensive attention as an effective modification strategy, yet a systematic review focusing on its working mechanism is insufficient. In this review, we analyze the influence of interfacial defects on carrier dynamic processes and comprehensively summarize the latest progress of interface engineering in PSCs from ETL/perovskite, HTL/perovskite, and CTL/electrode aspects. We highlight the key roles of interface engineering in rationalizing energy-level alignment, passivating defects, optimizing perovskite film quality, and improving device stability. We also provide general guidance for selecting appropriate interfacial strategies according to specific performance bottlenecks. Finally, the challenges and future perspectives of interface engineering toward high-performance PSCs are discussed.

TiO2-based colossal dielectric ceramics have emerged as a prominent research focus in recent years. However, their further applications have been constrained by several key limitations, including the requirement of high sintering temperature (>1400 degrees C), relatively high dielectric loss (>0.05, 1 kHz), and temperature stability (<200 degrees C). This study reports rutile (In0.5Ta0.5)(0.1)Ti0.87O1.88F0.12 ceramics at 1220 degrees C sintering using 12 % InF3 as the acceptor In3+ source, which exhibits a colossal dielectric constant (1.1 x 10(5)) and an ultra-low dielectric loss (0.0071) at 1 kHz and room temperature, even loss values below 0.04 (20 Hz - 100 kHz). Notably, the thermal stabilities (10 kHz, 100 kHz) simultaneously satisfy X9E (Delta epsilon(r)/epsilon(25) (degrees C) <= +/- 4.7 %) above 300 degrees C. F- not only supplies electrons to enhance the semiconductivity of grains, but also decreases the oxygen vacancy and average grain size (270 +/- 12.53 nm) to improve grain boundaries resistances, which reduces dielectric loss and enhances frequency and temperature stabilities. As a result, the dielectric mechanism is mainly related to internal barrier layer capacitor (IBLC) and high grain boundary resistance. Therefore, this strategy provides a creative design for developing TiO2-based ceramics.

The thermolabile polymer substrate of flexible perovskite solar cells (f-PSCs) enables defect formation during solution treatment and annealing. This phenomenon is unamiable to the device's efficiency and mechanical stability, which is the motivation of this work and drives the strategy regarding the multifunctional modification by introducing 7-amino-4-(trifluoromethyl)-2-benzopyrone (ATB) into the perovskite precursor solution. Results indicate that the ATB involvement contributes to the formation of high-quality perovskite films and passivates the defects in the perovskite film, extending the carrier lifetime and enabling a f-PSC with a power conversion efficiency (PCE) of 19.47%. The ATB participation also facilitates the bending stability of the flexible f-PSC device, where 89.1% of the initial PCE remains after 5000 bending cycles with a bending radius of 5 mm, compared to the 65.3% residual of the control device without ATB. Furthermore, the unencapsulated device exhibits an 82.8% remainder of the initial efficiency after 2100 h exposure at an ambient condition of 20 degrees C and 40 +/- 5% relative humidity more excellent than the control (68.4%). Hopefully, this work presents a fresh strategy in enhancing the mechanical stability of flexible f-PSC device with a decent PCE.

Nitrogen doped ZnO (ZnO:N), thin films have been deposited on glass substrate at the temperature of 350ºC by low cost homemade thermal spray pyrolysis (TSP) technique at a normal environmental conditions. In this study the average reflectance, transmittance and absorbance were measured (20%), (35%), and (45%), respectively. Absorption coefficient is 3.5x104cm-1 for N doped ZnO. Direct bandgap energy varies from 3.08-2.99eV and indirect band gap energy varies from 2.86-2.67eV for N doped ZnO. XRD analysis shows the (002) plane is present of samples and the average grain size decrease with increasing N concentration. Surface morphology of N doped ZnO films is studied by Scanning Electron Microscopy (SEM). It is seen that hexagonal crystal grains few voids are present for N doped ZnO samples. The surface exhibits more or less uniform surface morphology with some clusters on the whole surface. Hall Effect study confirms that Nitrogen doped ZnO (ZnO:N), thin films using Vander pauws method were made at room temperature at a constant field of 9.75 KG. Experimentally (1, 2, 3, and 4) % N doped ZnO thin films have shown in negative Hall Constant (RH). Which exhibited n-type characteristics. Hall Constant (RH), and Hall concentration (n), increases with increasing N doping concentration. Initially Hall mobility (μH), increases linearly for (1-2) % N doping concentration then it decreases for the rest of the doping concentration. We also found that the resistivity (ρ) decreases and the conductivity (s) increases with increasing N doping concentration which exhibits the semiconducting nature.

Iron pyrite is a cheap, stable, non-toxic, and earth-abundant material that has great potential in the field of photovoltaics. Electrochemical deposition is a low-cost method, which is also suitable for large-scale preparation of iron pyrite solar cells. In this work, we prepared iron pyrite films by electrochemical deposition with thiourea and explored the effect of sulfurization on the synthesis of high-quality iron pyrite films. Upon sulfurization, the amorphous precursor film becomes crystallized iron pyrite film. Optical and electrical characterization show that its band gap is 0.89 eV, and it is an n type semiconductor with a carrier concentration of 3.01 × 1019 cm−3. The corresponding photovoltaic device shows light response. This work suggests that sulfurization is essential in the electrochemical preparation for fabricating pure iron pyrite films, and therefore for low-cost and large-scale production of iron pyrite solar cells.

Despite having higher carrier mobilities and absorption coefficients of germanium (Ge) than those of silicon (Si), there has been less focus on Ge-based solar cells due to the low bandgap and high cost of Ge wafer as well as the requirement of its high-purity level. Currently, the availability of high-purity Ge (HPGe), the low-cost wafer slicing method, and proper design guidelines make it possible to design HPGe-based solar cells. Accordingly, in this article, we have designed and simulated a novel n-CdS/p-HPGe/p+-BaSi2 based npp+ double-heterojunction solar cell (DHJSC), where HPGe, cadmium sulfide (CdS), and orthorhombic barium disilicide (beta-BaSi2) have been used as the absorber, window, and back-surface field (BSF) layers, respectively. Using the solar cell capacitance simulator (SCAPS-1D), the effects of different physical parameters such as the thickness, doping, and defect densities, band offsets, and temperature on the photovoltaic (PV) parameters of the designed solar cells have been investigated systematically. This article renders the optimized PV parameters to improve the device performance with the highest power conversion efficiency (PCE) of -45.65% with a high open-circuit voltage of 1.16 V owing to the high built-in voltage of 1.7 V for the n-CdS/p-HPGe/p+-BaSi2 solar cells. This efficiency is almost consistent with the detailed balance limit for DHJSCs.

A comparative study with focusing on carrier recombination properties in Cu2ZnSn(S,Se)4 (CZTSSe) and the CuInGaSe2 (CIGS) solar cells has been carried out. For this purpose, electroluminescence (EL) and also bias-dependent time resolved photoluminescence (TRPL) using femtosecond (fs) laser source were performed. For the similar forward current density, the EL-intensity of the CZTSSe sample was obtained significantly lower than that of the CIGS sample. Primarily, it can be attributed to the existence of excess amount of non-radiative recombination center in the CZTSSe, and/or CZTSSe/CdS interface comparing to that of CIGS sample. In case of CIGS sample, TRPL decay time was found to increase with the application of forward-bias. This can be attributed to the reduced charge separation rate resulting from the reduced electric-field at the junction. However, in CZTSSe sample, TRPL decay time has been found almost independent under the forward and reverse-bias conditions. This phenomenon indicates that the charge recombination rate strongly dominates over the charge separation rate across the junction of the CZTSSe sample. Finally, temperature dependent VOC suggests that interface related recombination in the CZTSSe solar cell structure might be one of the major factors that affect EL-intensity and also, TRPL decay curves.

Temperature dependent time resolved photoluminescence (TR-PL) measurements have been performed in similar structured kesterite Cu2ZnSn(S,Se)(4) and chalcopyrite Cu(In,Ga)Se-2 thin film absorbers. It is investigated that at 26 K the measured lifetime values for a set of CZTSSe samples are more than one order magnitude higher than at room temperature whereas in CIGS this difference is not significant. At room temperature the significantly lower photoluminescence emission and minority carrier lifetime for CZTSSe comparing to CIGS suggest that the dominant non-radiative recombination processes are associated with CZTSSe than CIGS and it can limit the efficiency of CZTSSe based solar cells.

To determine the minority carrier lifetime, room temperature time-resolved photoluminescence (TR-PL) measurements have been performed on a set of Cu2ZnSn(S,Se)4 (CZTSSe) samples with different Cu/Sn ratios of 1.65, 1.75, and 1.85. TR-PL measurements were carried out on the bare CZTSSe thin films, CdS covered CZTSSe films and on solar cell structure using a femtosecond laser. The sample containing high Cu/Sn ratio of 1.85 shows the lowest lifetime, while films with Cu/Sn ratios of 1.65 and 1.75 show almost equal lifetime. The difference in lifetime between the CdS covered and solar structure samples is not remarkable. This demonstrates domination of recombination than charge separation by electric field. The bare films show extremely small lifetime. To examine surface quality, TR-PL emission spectra of uncovered CZTSSe and Cu(In,Ga)Se2 (CIGS) films were measured with two different excitation wavelengths of 420 and 750 nm, which generate excess carriers at different depths in absorbers. This comparison confirms the dominant surface recombination by CZTSSe than CIGS.

Cu2ZnSn(S,Se)4 (CZTSSe) thin films with various Cu/Sn ratio in the films have been investigated to study the effect of compositional variation over the electrical, optical, and structural properties of the film. Surface morphology and grain size were found to be significantly influenced by the Cu/Sn ratio in the films and grain size was found better for the samples with moderate Cu/Sn ratio of 1.75. Irrespective of the growth condition and compositional variation, all the CZTSSe crystals show that grains are oriented along (112) direction as evident from the room temperature XRD data. Dark current-voltage (I-V) curve reveals that that sample with Cu/Sn = 1.75 exhibits lowest leakage current, while sample with Cu/Sn = 1.85 has the highest leakage current along with larger ideality factor indicating larger recombination centers in this film. Series resistance was also found to be higher in the sample with higher Cu-content. An anomaly in the optical band-gap has been explained with the presences of impurity phases and compositional inhomogeneities in the CZTSSe materials.

Deep-level defects were investigated in Cu2ZnSn(S,Se)4 and Cu2ZnSnS4 thin-films using transient photocapacitance (TPC) spectroscopy. A deep-defect, OH1 centered around 1.0 eV above the valance-band (EV) of Cu2ZnSnS4 has been identified at room temperature (RT). However, OH1-defect could be identified in Cu2ZnSn(S,Se)4 at low temperature only. Absence of OH1-defect in Cu2ZnSn(S,Se)4 at RT explains its better performance comparing to Cu2ZnSnS4 solar-cell. A comparative study of the TPC spectra of the Cu(In,Ga)Se2 solar-cells was performed. Low intensity of defect-signal together with lower broadening of exponential band-tail in the TPC spectra were attributed to superior performance of Cu(In,Ga)Se2 solar-cells comparing to Cu2ZnSn(S,Se) counterpart.

Defect properties of Cu2ZnSn(Sx,Se1-x)4 (CZTSSe) were investigated by admittance spectroscopy (AS). Two defect states (labeled EA1 and EA2) were observed in CZTSSe (x=0.15) with different Cu/Sn ratio. When the Cu/Sn ratio increased from 1.75 to 1.95, the activation energy of EA1 and EA2 decreased and the defect densities increased. The capture cross sections of EA1 and EA2 defects are in the order from 10-16 cm2 to 10-18 cm2, indicating that these two defects possibly do not impact on device performance.

Room-temperature two-wavelength excited photoluminescence (PL) measurements have been performed in the kesterite Cu2ZnSnS4(CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) thin film absorbers. A defect level at 0.8 eV from the valence band and its properties are investigated. Two light sources of 635nm and 1550nm diode lasers, respectively, were used for above bandgap and 0.8eV defect level excitation. The two-wavelength excited PL intensity was stronger than that only above-gap laser irradiation for the CZTS specimen. This phenomenon strongly suggests that the 0.8eV defect level acts as recombination center at room temperature. On the other hand, this defect may act as a trap in lower gap CZTSSe.