Chaowei Xue

Partial shading is a common condition in the outdoor deployment of photovoltaic modules, potentially causing significant power loss and severe thermal damage. Limitations of existing solutions in balancing effect and cost necessitate a thorough solution, which involves a fundamental redesign at the solar cell level. Here we propose a cell architecture featuring integrated reverse conductivity to address this challenge. We derive the design principles by drawing inspiration from bypass diodes, and manage to introduce spatially uniform reverse conduction channels to the cell. These engineered in-cell channels exhibit bias-dependent switching behavior that enables reverse conductivity of the cell without compromising power conversion efficiency. The underlying mechanisms and modulation strategies of the cell are elucidated. Prepared photovoltaic modules composed of the proposed cells demonstrate clear advantages in thermal management and power output stability under partial shading conditions. The design principles and conduction channel strategies in this work also provide insight for other passivating-contact solar cells. The in-cell design approach offers merits in reliability, cost, and integration, and holds promise for next-generation photovoltaic technologies.

Silicon solar cells are essential for sustainable energy but remain limited by efficiency losses, particularly in the fill factor^1,2,3. Here we develop a hybrid interdigitated back-contact solar cell that combines advanced all-surface passivation with laser-treated tunnelling contacts. This approach achieves a power conversion efficiency of 27.81%, approaching 95% of the theoretical limit⁴. By integrating high- and low-temperature processes, we suppress recombination and enhance contact performance, achieving a fill factor of 87.55%—nearly 98% of the theoretical limit. A model links the ideality factor to carrier loss mechanisms, elucidating carrier recombination in both the bulk and the surface and clarifies key fill factor losses owing to recombination. These innovations provide both experimental and theoretical advances towards scalable, high-efficiency silicon photovoltaics.

Achieving highly ordered and uniformly covered self-assembly monolayers (SAMs) with optimal packing configuration on textured silicon substrates remains a critical challenge for further improving the efficiency of perovskite/silicon tandem solar cells (TSCs)^1-3. Here we design an asymmetric SAM (named as HTL201) featuring anchoring group and spacer flanking a carbazole core, serving as hole selective layer (HSL) for perovskite/silicon TSCs. When compared to symmetric SAMs with nitrogen-bonded phosphonic acid group, the HTL201 molecule exhibits minimized steric hindrance and improved coverage on the transparent conductive oxide (TCO) recombination layer. The strong coordination interaction between HTL201 and perovskite film effectively reduces non-radiative recombination at buried interface. Notably, the optimized energy level alignment between perovskite and HTL201, accompanied by an increase in quasi-Fermi level splitting (QFLS) value of the perovskite layer, enables an impressive voltage of nearly 2 V for perovskite/silicon TSCs, resulting in a certified power conversion efficiency (PCE) of up to 34.58% based on a silicon heterojunction (SHJ) solar cell.

Crystalline-silicon heterojunction back contact solar cells represent the forefront of photovoltaic technology, but encounter significant challenges in managing charge carrier recombination and transport to achieve high efficiency. In this study, we produced highly efficient heterojunction back contact solar cells with a certified efficiency of 27.09% using a laser patterning technique. Our findings indicate that recombination losses primarily arise from the hole-selective contact region and polarity boundaries. We propose solutions to these issues and establish a clear relationship between contact resistivity, series resistance, and the design of the rear-side pattern. Furthermore, we demonstrate that the wafer edge becomes the main channel for current density loss caused by carrier recombination once electrical shading around the electron-selective contact region is mitigated. With the advanced nanocrystalline passivating contact, wafer edge passivation technologies and meticulous optimization of front anti-reflection coating and rear reflector, achieving efficiencies as high as 27.7% is feasible.

Back contact silicon solar cells, valued for their aesthetic appeal by removing grid lines on the sunny side, find applications in buildings, vehicles and aircrafts, enabling self-power generation without compromising appearance^1-3. Patterning techniques arrange contacts on the shaded side of the silicon wafer, offering benefits for light incidence as well. However, the patterning process complicates production and causes power loss. Here we employ lasers to streamline back contact solar cell fabrication and enhance power conversion efficiency. Our approach produces the first silicon solar cell to exceed 27% efficiency. Hydrogenated amorphous silicon layers are deposited on the wafer for surface passivation and collection of light-generated carriers. A dense passivating contact, diverging from conventional technology practice, is developed. Pulsed picosecond lasers at different wavelengths are used to create back contact patterns. The developed approach is a streamlined process for producing high-performance back contact silicon solar cells, with a total effective processing time of about one-third that of emerging mainstream technology. To meet terawatt demand, we develop rare indium-less cells at 26.5% efficiency and precious silver-free cells at 26.2% efficiency. The integration of solar solutions in buildings and transportation is poised to expand with these technological advancements.

Silicon solar cells are a mainstay of commercialized photovoltaics, and further improving the power conversion efficiency of large-area and flexible cells remains an important research objective^1,2. Here we report a combined approach to improving the power conversion efficiency of silicon heterojunction solar cells, while at the same time rendering them flexible. We use low-damage continuous-plasma chemical vapour deposition to prevent epitaxy, self-restoring nanocrystalline sowing and vertical growth to develop doped contacts, and contact-free laser transfer printing to deposit low-shading grid lines. High-performance cells of various thicknesses (55–130 μm) are fabricated, with certified efficiencies of 26.06% (57 μm), 26.19% (74 μm), 26.50% (84 μm), 26.56% (106 μm) and 26.81% (125 μm). The wafer thinning not only lowers the weight and cost, but also facilitates the charge migration and separation. It is found that the 57-μm flexible and thin solar cell shows the highest power-to-weight ratio (1.9 W g⁻¹) and open-circuit voltage (761 mV) compared to the thick ones. All of the solar cells characterized have an area of 274.4 cm², and the cell components ensure reliability in potential-induced degradation and light-induced degradation ageing tests. This technological progress provides a practical basis for the commercialization of flexible, lightweight, low-cost and highly efficient solar cells, and the ability to bend or roll up crystalline silicon solar cells for travel is anticipated.

The development of high efficiency Si solar cells is seeing successful industrialization of carrier-selective and passivating contact technologies, including Tunnel Oxide Passivated Contact (TOPCon) and Silicon Heterojunction Technology (SHJ). Driven by cell technology innovation, the Si PV industry is making bold moves to see 26-27% efficiencies in mass production in the coming years. Undisputablly, Si wafer development provides strong support for the fast-upgrading cell technologies, and guarantees the technologies' deployment at affordable costs. To date, p-type Si wafer is dominating the market by 95% market share. However, a 5% to 50% uptaking of n-type Si wafer is predicted by ITRPV. One critical factor for this judgement is that the n-type Si solar cell efficiencies are leading ahead that of the p-type. It is well argued that the n-type Si wafer manufacturing can steadily ramp up given the demand, and the cost disadvantage can be alleviated to some extent with scaled production capacity. At the same time, the industry shall not ignore the inherent cost advantage of p-type wafers, and keep exploiting the possibilities to push up the p-type Si solar cell efficiency. In this work, we demonstrate that the p-type SHJ solar cell efficiency can reach 26.6%, which is just 0.2% behind of its n-type counterpart. This result establishes a solid foundation for further SHJ technology development on a cost-effective basis.