Matthieu Despeisse

As global decarbonization accelerates the need for extensive solar photovoltaic deployment, land‐use conflicts have become increasingly pressing. Integrating PV into the built environment emerges as an effective strategy to mitigate these challenges by generating electricity where it is consumed. However, the polymeric encapsulant—a core material in photovoltaic (PV) modules—introduces critical fire safety concerns, particularly in building applications with strict regulatory requirements. This review addresses the issue with a dual approach. First, it presents various solutions to mitigate fire hazards, such as the incorporation of flame retardants, and defines five families of the latter solutions. Despite the central role of the encapsulant in module flammability, little research has focused on the use of flame retardants in photovoltaic modules. Then, a review of the existing standards and testing approaches that can be used for the assessment of building‐integrated photovoltaic fire safety is presented. Based on the findings, a methodology for the evaluation of the fire performance is also proposed, with this framework evaluated at both the material and module levels.

In this article, transfer length method (TLM) measurements under variable illumination are applied to study p-type carrier selective passivating contacts (CSPCs) employed in the silicon heterojunction (SHJ) technology. In the case of p-type CSPCs deposited on p-type crystalline silicon (c-Si(p)) wafers, we demonstrate that illumination has a strong impact on the contact resistivity ( $\rho _{c}$ ) value, as demonstrated in our previous contribution in the case of n-type CSPCs on c-Si(n). Noticeably, it was again found that $\rho _{c}$ increases and that the c-Si sheet resistance ( $R_\text{sh}$ ) decreases with the illumination. In addition, we demonstrate that $\rho _{c}$ is impacted differently by illumination depending on the doping of the p-type thin hydrogenated silicon layer. Then, we investigate and discuss the applicability of TLM measurements under illumination to measure p-type CSPCs deposited on their inverse type c-Si(n) wafers. First, performing TLM measurement in dark conditions of such samples allow one to measure $R_\text{sh}$ values with orders of magnitude corresponding to the c-Si(n) inversion layer one. Second, we demonstrate that under illumination, the lateral transport inside the c-Si(n) bulk is supported by the electrons thanks to two experimental evidences, i.e., that the $R_\text{sh}$ behavior as a function of injection behaves as the one of electrons and that an electron transport inside the c-Si(n) wafer in the presence of two p-type CSPCs TLM pads can only be mediated thanks to photogeneration under one pad and recombination under the other. These results provide additional understandings of the TLM measurement under illumination as well as strong insights for the investigation of carriers' transport and electrical losses in CSPCs solar cells.

We investigate the effect of light soaking and forward electric bias treatment on silicon heterojunction solar cells and modules and, in particular, the influence of the thermal treatment occurring during lamination. A substantial performance increase is observed after electric bias or light soaking, which is shown to be potentially partly reset by the lamination process. This reset is reproduced by annealing the cells with the same thermal budget. A second treatment after lamination again improves performances, and a similar final performance is reached independently of the prelamination treatment. Therefore, a single treatment after lamination enables maximal module output with no benefit from a cell pretreatment. Whereas the cells react overall better to forward bias, the modules show a slightly better response to light soaking.

For the current PV production about 2000 tons of silver are consumed per year, 10% of the entire world annual silver supply. The PV production is expected to grow significantly in the next decades in order to enable the energy transition to 100% renewables. Annual production volumes in the terawatt range are predicted already for 2030 and this may lead to higher silver price and put more pressure on the industry to replace silver by copper. Within the Ameliz project several patterning approaches for copper electrodeposition on heterojunction cells are developed: firstly, patterning by printing a metal seed grid with a dielectric layer as plating mask and secondly masking by a monolayer of self-assembling molecules. These molecules consist of a phosphonic acid group and a hydrocarbon chain. They are bonded to the ITO surface and form a monolayer of well-ordered, densely packed hydrophobic chains, which protects the ITO surface against plating solutions. Furthermore, methods for selective formation of a copper seed layer by electrografting and for improved adhesion by ITO reduction are being investigated.

Providing state‐of‐the‐art surface passivation and the required carrier selectivity for both contacts, hydrogenated amorphous silicon thin films are the key components of silicon heterojunction (SHJ) solar cells. After intensive optimization of these layers for standard front and back contacted (FBC) n‐type cells, high surface passivation levels were achieved on cell precursors, demonstrated by minority carrier lifetimes exceeding 18 ms on float‐zone (FZ) and 11 ms on Czochralski (Cz) c‐Si wafers. The application of these very same layers on cheaper and commercially available Cz p‐type wafers resulted in similar passivation quality, with lifetimes above 10 ms as well. Large‐area industrial bifacial FBC SHJ cells processed on wafers taken along the full length of a high‐resistivity Cz p‐type ingot showed efficiencies in the 22.5% to 23% range, significantly higher than previously reported results on such substrates and on par with their n‐type counterparts. Best efficiencies on large‐area monofacial devices (>220 cm²) are 23.6% on Cz p‐type and 24.4% on Cz n‐type, similar to certified results obtained on lab‐scale cells (4 cm²), 23.76% on FZ p‐type and 24.21% on FZ n‐type. Notably, no specific adaptation of the reference n‐type cell process was necessary to achieve these results on p‐type material. Additionally, a 25% certified efficiency has been obtained on medium‐sized (25 cm²) interdigitated back‐contacted SHJ cells, featuring the same passivation layers developed for FBC devices. These results illustrate the versatility of the SHJ technology for various high‐efficiency screen‐printed solar cell configurations and show possible ways to improve its competitiveness on the global photovoltaic market.

Broadband transparent and highly conducting electrodes are key to avoid parasitic absorption and electrical losses in solar cells. Here, we propose zirconium-doped indium oxide (IO:Zr) as a transparent electrode intrinsically meeting both requirements and demonstrate its application as the front electrode in silicon heterojunction (SHJ) solar cells. The exceptional properties of this material rely on the combination of high-doping and high electron mobilities, achieving with this a wide optical band gap (3.5–4 eV), low free carrier absorption, and high lateral conductivity. A single film of IO:Zr has an electron mobility of 100 cm2/Vcs with a carrier density of 2.5–3 × 1020 cm–3, resulting in a sheet resistance of around 25 Ω/sq for 100-nm-thick films. Their implementation as a front electrode in SHJ solar cells results in an important gain in current density as compared to the standardly used Sn-doped indium oxide. This is due to reduced parasitic absorption in both, the UV and IR, as confirmed by external quantum efficiency measurements. SHJ devices with the optimized IO:Zr front electrode, resulting in current densities of 40 mA/cm2, a fill factor of 80%, and a conversion efficiency of 23.4%.

We present an electrical model developed with LTSPICE that simulates the performance of a string of cells with disconnections in the electrical circuit. In a previous contribution, we quantified experimentally how the module performance is affected when one or more ribbons are cut or disconnected between cells. The measurements were made on mini-modules (strings) of six cells, connected in series by three interconnection ribbons. Here, we use these experimental results to validate our model. Results show that our model is able to describe well the power reduction due to the interruption/removal of the cell interconnecting ribbons, and to reproduce the peculiar shape of the IV curves of a string affected by non-homogeneous distribution of the series resistance within some of the cells.

We applied hydrogen passivation, gettering and a combination of both to quasi-mono (qm) wafer material to enhance its bulk lifetime and prepared silicon heterojunction (SHJ) solar cells. We find that while our applied hydrogen passivation alone seems not to enhance lifetime, a gettering treatment increases bulk lifetime so that efficiencies up to 21.5% were achieved with a SHJ solar cell. This is close to the highest efficiency reported for such a cell. We find that the variation of the absorber thickness plays a minor role for the investigated solar cells and that similar efficiencies could have been obtained for Cz and gettered qm wafers. The latter is mainly due to the fact that the higher efficiency potential of the Cz material could not be fully exploited due to a degradation of surface passivation during the sputtering of the TCO on the cell, which could not be fully recovered in the final annealing step.