Periodic hexagonal microtexture arrays (also known as honeycombs) are successfully implemented for the first time in a superstrate glass configuration. Hexagonal textures on glass demonstrate an anti-reflective effect when compared to flat glass. It is shown that light scattering increases at the honeycomb interfaces with an increase in texture height and periodicity. The performance of the textures is demonstrated using thin-film single-junction PV devices based on an indirect bandgap semiconductor material, nanocrystalline silicon (nc-Si:H), which requires light trapping in the infrared region of the spectrum. Inspecting the nc-Si:H bulk absorber suggests a conformal, crack-free growth of crystals on the hexagonal arrays. Short-circuit current density (J_SC) increases with an increase in the aspect ratio of the superstrate, without compromising voltage and fill factor. The J_SC enhancement is attributed to a combined benefit of (i) the anti-reflective nature of developed textures, (ii) trapping light within the absorbing layer through multiple order diffraction at the front and (iii) reflection from a back reflector with adapted hexagonal morphology. With the above observations, a J_SC of 28.6 mA/cm² (photovoltaic conversion efficiency of 9.3 %) is achieved for a 5μm periodic texture with a height of 1μm (aspect ratio = 0.21). This is the highest reported J_SC for a single-junction nc-Si:H solar cell in a superstrate configuration without an external anti-reflection coating.

Accurate prediction of optical performance in solar cells with multiscale-textured interfaces is essential for optimizing light management in next-generation photovoltaics. For the first time, a systematic validation of two complementary modeling approaches is carried out on experimentally fabricated thin-film silicon (TF Si) solar cells: rigorous coupled-wave analysis (RCWA), offering a full electromagnetic solution but constrained by boundary conditions, and a ray optics model, operating in the refractive regime. The study involves two device architectures: an a-Si:H single-junction cell on commercial Asahi VU-type glass with random nanotextures, and an nc-Si:H single-junction cell on novel micro-periodic honeycomb-textured glass developed in-house. Simulated and measured external quantum efficiency (EQE) and total front reflection losses (1-R) are benchmarked using the root mean squared error (RMSE). The ray model shows deviations of only 2%–6%, comparable to RCWA, while reducing computation time from 1 week to less than 30 min. Applied to an a-Si:H/nc-Si:H tandem device on honeycomb-textured glass, ray optics reproduced the optical response with spectral deviations below 6% and photocurrent mismatch under 0.2 mA/cm2. These findings uniquely establish ray optics, when combined with accurate optical constants and realistic interface morphologies, as a reliable and computationally efficient predictive tool broadly transferable to thin-film technologies, including perovskites.

Techniques to facilitate excellent optical yield are required to manufacture high-performing solar cells. In thin-film solar cells, light scattering with the help of textured interfaces increases the absorption path length of photons and reduces the reflection of the photovoltaic active layer. These textures should also facilitate the growth of crack-free thin-film layers, ensuring high efficiency in multijunction devices. This work explores three texturing methods for glass that have the potential to be integrated into solar cells in a superstrate configuration. A detailed study of sacrificial texturing on glass using i-ZnO ((Formula presented.)) and indium-doped tin oxide ((Formula presented.)) is presented. The optical interaction of these textures is correlated to their root-mean-square (RMS) roughness ((Formula presented.)). It is demonstrated that high optical scattering can be achieved for both (Formula presented.) and (Formula presented.) but at different (Formula presented.) regimes. A novel texture with superimposed morphology, named superimposed sacrificial texturing ((Formula presented.)), is created by combining (Formula presented.) and (Formula presented.) through sequential wet etching. The (Formula presented.) exhibits exceptional transmission and light scattering properties. Nanocrystalline silicon (nc-Si:H) single-junction solar cells were fabricated in a superstrate configuration to investigate the impact of these textures on indirect bandgap thin-film solar cells. The efficiency of solar cells on (Formula presented.) is nearly 0.57% and 1.52% (absolute) more than (Formula presented.) and (Formula presented.) solar cells, respectively. By superimposing two textures, solar cells can combine the advantages of enhanced optical performance with high-quality nc-Si:H material growth.

This study investigates the transparent conductive oxides (TCOs) as front contact for thin-film solar cell applications by developing a bilayer design that decouples the optical and electrical functionalities. The bilayer front contact structure combines hydrogenated indium oxide (IOH) and non-intentionally doped zinc oxide (ZnO) materials. This design achieves enhanced optoelectrical properties with a mobility of 120 cm²/Vs and a carrier density of 1.97·10¹⁹ cm^-3. Notably, the bilayer outperforms the expected average of its constituent layers in both transparency and conductivity, reflecting the benefits of optimized layer architecture. When integrated as the front electrode in a hydrogenated nanocrystalline silicon (nc-Si:H) solar cell, the IOH/ZnO bilayer yields a fill factor of 64.56 % and a power conversion efficiency of 7.85 %. When using an ITO front contact, the nc-Si:H solar cell reveals a fill factor of 56.27 % and an efficiency of 6.80 %. By successfully decoupling optical and electrical properties, the optimized IOH/ZnO bilayer offers a significant advancement over single-layer TCO configurations, presenting an innovative pathway for enhanced performance in thin-film solar cell technology.

This study investigates the influence of reactive sputtering gas composition, specifically the oxygen-to-argon (O2/Ar) and hydrogen-to-argon (H2/Ar) ratios, on the optoelectrical and structural properties of fluorine-doped tin oxide (FTO) and undoped tin dioxide (SnO2) thin films deposited at room temperature (RT). Through systematic variation of O2 and H2 content in the sputtering atmosphere, gas-phase composition is correlated with key performance metrics, including optical transmittance, sheet resistance, carrier density, and mobility, both before and after postdeposition annealing (PDA) at 400 °C in a nitrogen atmosphere. An optimal O2/Ar ratio of 0.3–0.4% achieves the best optoelectrical trade-off in FTO, yielding a minimum sheet resistance (468 Ω/sq) and high mobility (13.7 cm2/(V s)). In SnO2 films, increasing oxygen improves optical transparency but reduces conductivity, while hydrogen incorporation at fixed 1% O2/Ar enhances transparency and lowers sheet resistance in the as deposited state. These effects are attributed to defect passivation rather than changes in oxidation state, as supported by X-ray photoelectron spectroscopy results. Ambipolar conduction observed in the as deposited films transitions to stable n-type behavior after PDA, highlighting the role of thermal treatment. Although RT sputtered SnO2-based films do not yet match the performance of high-temperature grown benchmarks, these findings demonstrate that careful tuning of the sputtering gas composition enables scalable, thermally compatible, and cost-effective fabrication of transparent conducting electrodes and transport layers in photovoltaic applications.

Textured glass is used in a wide range of applications to improve optoelectrical performances, such as photovoltaics, biosensing, microfluidics, and photonics. Honeycomb textures have demonstrated an excellent performance in optical devices using crystalline silicon wafers as opaque substrates. As a pathway to translate these advantages to configurations implementing glass, hexagonal-shaped microsized craters (honeycombs) are made on glass in this study. We use photolithography combined with wet etching for this process. The relationship between photoresist mask design, glass–photoresist adhesion, wet-etching steps, and the mechanism of honeycomb formation is studied. It is demonstrated that the higher the isotropic nature of etching achieved, the deeper the hexagonal craters will be. The potential of hexagonal textures on glass to significantly reduce reflection to <8% over the entire spectral range is observed. Finally, hexagonal microsized textures with 5 μm periodicity and 1.01 μm depth that effectively diffuse 50% of the total transmitted light at near-infrared (1100 nm) wavelengths are developed.

Photovoltaic (PV) panel installations in buildings and transportation hubs pose additional safety challenges as the glare from the panels can impose adverse impacts like flash blindness in human eyes. This study substantiates that polymer encapsulated thin film modules offer significantly low glare levels that are essential for building integrated and transport hub installations. In this work, the glare hazard potential associated with matt ethylene tetrafluoroethylene (ETFE)-based polymer sheet used as the frontsheet for the production of flexible thin amorphous silicon (a-Si) PV modules is studied and compared with standard PV glass used in crystalline silicon (c-Si) PV panels. The specular reflectance extracted from the measured total and diffuse reflectance for an angle of incidence (AOI) of 8° and the angular intensity distribution (AID) of specular reflectance measured for AOI ranging from 10° to 80° are utilized for glare assessment of the frontsheets. The mean value of specular reflectance extracted from the measured total and diffused reflectance is as low as 0.5% for the polymer frontsheet and is 4% for glass. The AID measurements suggest that the reflection from the polymer frontsheet is highly diffusive in nature in contrast to glass and the measured specular reflectance is always close to a magnitude lower than that from glass for all AOI. With the increase in AOI, the specular AID reflectance increases exponentially for glass to become as high as 40%, which is almost 20 times less than that from the polymer frontsheet for an AOI of 80°. Further, the c-Si test structure with glass and thin a-Si PV module with matt ETFE-based polymer as frontsheet showed similar specular reflectance trends as that of glass and the polymer frontsheet, respectively.

Our study focuses on the optimization of front contact design by exploring a novel bilayer configuration that employs transparent conductive oxides (TCOs) to enhance the efficiency of thin-film silicon solar cells. The TCOs investigated include sputtered hydrogenated indium oxide (IOH), cerium-doped indium oxide (ICO), cerium and hydrogen co-doped indium oxide (ICOH), and intrinsic zinc oxide (i-ZnO). We highlight the suitability of these TCOs in a bilayer design, first analyzing their opto-electrical properties as monolayers and subsequently in bilayer configurations. The IOH/i-ZnO bilayer architecture, in particular, demonstrates promising opto-electrical properties on both flat glass and micro-textured glass substrates. IOH/i-ZnO on flat glass substrate demonstrates remarkable mobility (143.44 cm²/Vs) and a carrier concentration in the order of 10¹⁹cm^-3. The mean of reflectance (R) trends consistently exceeds 80%, while the mean of transmittance (T) trends falls below 20% beyond 500 nm. The interference effects within the bilayers are minimized for designs on micro-textured glass, preserving values within a desirable range. These findings represent an innovative approach to front contact design for thin-film silicon solar cells, emphasizing the potential of bilayer configurations to advance solar cell technology.

To boost the efficiency of perovskite solar cells beyond the limit of a single-junction cell, tandem cells are employed, requiring low bandgap materials. This is realized by partially substituting lead(II) (Pb2+) with tin(II) (Sn2+) in the perovskite structure. In this work, a scalable method is presented to produce formamidinium lead tin iodide (FAPb0.5Sn0.5I3) films by sequential thermal evaporation (sTE) of PbSnI4, which is an alloy of SnI2 and PbI2, and FAI, in vacuum. Annealing at 200 °C yields a highly oriented and crystalline layer comprising grains over 1 µm on average. Photoconductance measurements reveal carrier lifetimes exceeding 2 µs and mobilities ≈100 cm2/(Vs). Structural analysis confirms that, while interdiffusion is abundant even at room temperature, the complete conversion requires high temperatures. Although the incorporation of Cs+ into the A-site of the perovskite increases the grain size, charge carrier dynamics are reduced. A comparison between the sTE films and spin-coated samples of the same composition demonstrates the superior photoconductance of the sTE films, without the need for any additives. Overall, this study showcases the potential of sTE for producing high-quality low band gap (LBG) perovskite materials.

Silicon heterojunction (SHJ) solar cells have achieved a record efficiency of 26.81% in a front/back-contacted (FBC) configuration. Moreover, thanks to their advantageous high V_OC and good infrared response, SHJ solar cells can be further combined with wide bandgap perovskite cells forming tandem devices to enable efficiencies well above 33%. In this study, we present strategies to realize high-efficiency SHJ solar cells through combined theoretical and experimental studies, starting from the optimization of Si-based thin-film layers to the implementation of electrodes with reduced indium and silver usage. Advanced opto-electrical simulations, which enable comprehensive theoretical understandings of the main physical mechanisms governing carriers’ collection and light management, provide clear pathways for device designs and experimental optimizations. We present the fabricated FBC-SHJ solar cells in both monofacial and bifacial configurations with the best efficiencies of 24.18% and 23.25%, respectively. We point out that to achieve optimum device performance, the compositional materials should be holistically optimized and evaluated as part of the contact stacks with adjacent layers. As an outlook beyond the classical FBC-SHJ solar cell architecture, we propose various novel SHJ-based solar cell architectures. Their potential performance was assessed and compared via rigorous opto-electrical simulations and a maximal efficiency of 27.60% was simulated for FBC-SHJ solar cells featuring localized contacts.

Transparent conductive oxides (TCOs) are used as front electrode of thin film silicon (TF-Si) solar cells to increase power conversion efficiency. Metal oxides doped with different materials can be deployed as TCO. The preferred TCO is usually selected using a trade-off between transparency and conductivity. This work proposes a bi-layer front contact to address the limitation of this trade-off. IOH and i-ZnO are chosen as the best candidates for such architecture due to their good opto-electrical properties. A thin layer of IOH ensures good lateral conductivity and high transparency in the visible part of the solar spectrum. An additional i-ZnO layer provides minimized parasitic absorption losses along with low transverse resistivity. The best opto-electrical properties are achieved when deposition temperature and power density are set at 25°C and 1.5 W/cm², 200°C and 2 W/cm² for IOH and i-ZnO respectively.

Accelerating the deployment of Photovoltaic (PV) systems is a key contributing factor in achieving climate neutrality. Even though solar power is one of the cheapest energy sources and its deployment is growing rapidly around the world, an even faster growth is required to achieve existing climate goals. Besides the role that finance and permitting can play as enablers or barriers to this, the key elements to enable fast PV deployment are the use of education, and science and data-driven tools to empower citizens, installers, and investors to make their decisions based on robust scientific evidence. This perspective article aims to summarize the key concepts presented and discussed during the side event at COP27 on PV resources towards climate neutrality. The article will accomplish this by highlighting two key aspects: (1) the advantages of using solar-related education and data-driven tools, and (2) showcasing the significance of education, improved data and tools, community involvement, and PV mapping in expediting the deployment of PV systems.

In this study, undoped hydrogenated amorphous silicon (a-Si:H) thin films deposited under moderate dilution ratios of silane by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) have been investigated using steady-state photoconductivity and improved dual beam photoconductivity (DBP) methods to identify changes in multiple gap states in annealed and light-soaked states. Four different gap states were identified in annealed state named as A, B, C, and X states. The peak energy positions of these Gaussian distributions are consistent with those recently identified by Fourier transform photocurrent spectroscopy (FTPS). After in situ light soaking, their density increases with different rates as peak energy positions and half-widths remain unaffected. The electron-occupied A and B states located below the dark Fermi level and their density and ratios in the annealed and light-soaked states correlate well with those defects detected by time-domain pulsed electron paramagnetic resonance (EPR) experiments. The A, B, and X states located closer to the middle of the bandgap anneal out at room temperature in dark and define the "fast"states. However, the C states show no sign of room temperature annealing such that they must define the "slow"states in undoped a-Si:H. The results found in this study indicate that the anisotropic disordered network is a more appropriate model than previously proposed defect models based on the continuous random network to define the nanostructure of undoped a-Si:H, where multiple defects, D0 and non-D0 defects, can be identified by using the improved DBP method.

We extended the capabilities of our GenPro4 solar cell optical model, making it an even more powerful tool for nanotexture optimization. We show its application to thin-film CIGS, silicon, and perovskite/silicon tandem solar cells.

Surface textures that result in high optical yields are crucial for high efficiency photovoltaic (PV) devices. In this work three different texturing approaches are presented that result in smooth concave structures devoid of sharp features. Such features can sustain the crack-free growth of device quality nano- to poly-crystalline materials such as nano-crystalline silicon, perovskites or C(I)GS, facilitating routes towards hybrid multijunction PV devices. A sacrificial implanted poly-c-Si layer is used to develop a random surface texture for the first texturing approach (Tsac). The influence of the processing conditions, such as layer thickness, implantation energy, dose and ion type, annealing time and temperature, of the sacrificial layer on the developed surface features is investigated. Additionally, a photolithographically developed honeycomb texture (Thoney) is presented. The influence of mask design on the honeycomb features is discussed and a relation is established between the honeycomb period and crack formation in nano-crystalline silicon layers. The reflective properties (spectral reflection, haze in reflection and angular intensity distribution) of these approaches are characterized and compared to a third texturing approach, Tsp, the result of chemically smoothened pyramidal <111> features. It was demonstrated that high optical scattering yields can be achieved for both Thoney and Tsp. Additionally, the performance of a-Si/nc-Si tandem devices processed onto the different textures is compared using both optical device simulations and real device measurements. Simulations demonstrate strong improvements in Jsc-sum (≈45%), in reference to a flat surface, and high Voc*FF of over 1 V are demonstrated for Tsp.

In this paper the opto-electrical nature of hydrogenated group IV alloys with optical bandgap energies ranging from 1.0 eV up to 2.3 eV are studied. The fundamental physical principles that determine the relation between the bandgap and the structural characteristics such as material density, elemental composition, void fraction and crystalline phase fraction are revealed. Next, the fundamental physical principles that determine the relation between the bandgap and electrical properties such as the dark conductivity, activation energy, and photoresponse are discussed. The unique wide range of IV valence alloys helps to understand the nature of amorphous (a-) and nanocrystalline (nc-) hydrogenated (:H) germanium films with respect to the intrinsicity, chemical stability, and photoresponse. These insights resulted in the discovery of i) a processing window that results in chemically stable Ge:H films with the lowest reported dark conductivity values down to 4.6·10^-4 (Ω ·cm)^-1 for chemical vapor deposited Ge:H films, and ii) O, C and Sn alloying approaches to improve the photoresponse and chemical stability of the a/nc-Ge:H alloys.

The oxidation and carbisation kinetics of porous amorphous and nano-crystalline hydrogenated germanium (a-Ge:H and nc-Ge:H) films exposed to ambient air and deionized water have been studied using vibration modes observed by infrared spectroscopy. Based on infrared analysis, a two-step process of first oxidation by water and secondly carbisation by carbon dioxide (CO2) is proposed that partly mimics the (photo-)catalytic processes in artificial (photo)synthesis. It is shown that water acts like the precursor for oxidation of porous a-Ge:H and nc-Ge:H in the first step. The incorporation of oxygen in a-Ge:H and nc-Ge:H alloys occurs preferentially at Ge-dangling bonds and not at the Ge–Ge back bonds like in hydrogenated silicon alloys (next of kin IV-valence element). The formation of germanium oxide (GeO) tissue at void surfaces locally creates Ge alloys with significantly lower energy levels for the valence band that can align with the half reaction for water reduction. The heterogeneous nature of a-Ge:H and nc-Ge:H oxidation will result in local catalytic generation of electrons and protons. It is proposed that these charge carriers and ions act as precursors for the second-step reaction based on carbisation that includes both the adsorption of CO2 and formation of CO and formaldehyde.

Two terminal multi-junction (MJ) photovoltaic (PV) devices are well established concepts to increase the solar-to-electrical power conversion in reference to single PV junctions. In multi-junction PV devices two consecutive sub-cells are interconnected using a tunnel recombination junction (TRJ) in which the light excited holes of one sub-cell recombine with the light excited electrons of the other sub cell. An ideal TRJ is an ohmic contact with non-rectifying behaviour. TRJ's based on p- and n-doped silicon-oxides have been successfully applied in a variety of hybrid multi-junction PV devices in which tunnelling and trap-assisted tunnelling over width of 5–20 nm rules the TRJ's recombination kinetics. In this contribution the qualitative fundamental working principles of tunnel recombination junctions based on p- and n-doped silicon and silicon-oxide alloys are revealed using both electrical modelling and experiments based on a unique set of tandem lab cells (four types based on four different PV materials) combined with structural variations in TRJ architectures. The study results in design rules for the integration of silicon-oxide based TRJ's and provides fundamental insights into the sensitivity of the electrical performance of the TRJ's to doping concentrations, to alignment of the conduction and valence bands of consecutive sub-cells, to the nature of interface defects, to the growth of amorphous and crystalline phases and its dependence on substrate or seed layers and to the nanoscale thicknesses of the TRJ layers.

A logical next step for achieving a cost price reduction per Watt peak of photovoltaics (PV) is multijunction PV devices. In two-terminal multijunction PV devices, the photo-current generated in each subcell should be matched. Intermediate reflective layers (IRLs) are widely employed in multijunction devices to increase reflection at the interface between subcells to enhance current generation in the subcell(s) positioned before the IRL, in reference to the incident light. In this work, the results of over 65 multijunction devices are presented, in order to explore the effect of different current matching approaches. The influence of variations in absorber thickness as well as thickness variations of different IRLs based on silicon-oxide, various transparent conductive oxides (TCO), and metallic layers on all-silicon multijunction PV devices is studied. Specifically, hybrid, 2-terminal, monolithically integrated silicon heterojunction (SHJ) and thin film nanocrystalline silicon (nc-Si:H) and amorphous silicon (a-Si:H) tandem and triple junction devices are processed. Based on these experiments, certain design rules for optimal current matching operation in multijunction devices are formulated. Finally, taking these design rules into account, record all-silicon multijunction devices are processed. Conversion efficiencies close 15% and (Formula presented.) V are demonstrated for triple junction SHJ/nc-Si:H/a-Si:H devices. Such conversion efficiencies for a wireless, high-voltage wafer-based all-silicon 2-terminal multijunction PV device opens the way for efficient autonomous solar-to-fuel synthesis systems as well as other wireless innovative approaches in which the multijunction solar cell is used not only as a photovoltaic current-voltage generator, but also as an ion-exchange membrane, electrochemical catalysts, and/or optical transmittance filter.

In this abstract an overview is presented of research performed in the DISCO project, on the development of a silicon-based high voltage multijunction device for autonomous solar to fuel applications.'