Search

Over the past few years, perovskite solar cells have arisen as a technology to potentially side with mainstream silicon photovoltaics (PVs) to help drive the transition towards renewable sources of energy. The coupling of perovskites with silicon in a tandem configuration may accelerate this development due to the remarkably high power conversion efficiencies possible with such devices. However, most of the perovskite/silicon tandem achievements so far have been confined to the lab environment, with only a few reported tests under outdoor conditions, using packaged devices. Nevertheless, one of the major challenges for perovskite/silicon tandem technologies, in addition to scale‐up, lies in the cell‐to‐module (CTM) translation, which for the perovskite/silicon tandem concept is complicated by perovskite‐imposed constrains such as a low‐temperature resilience, imposing challenges regarding tabbing and lamination, as well as a high sensitivity to moisture ingress, mandating the search for adequate encapsulation materials and methods. Herein, these challenges are described and assessed in depth and a perspective on future directions toward module design, tailored for perovskite/silicon tandem PVs is given, combining high performance with excellent durability. The discussion also holds relevance for all‐perovskite and other emerging PV technologies seeking market entry. [ABSTRACT FROM AUTHOR]

Amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers-- inserted between substrate and (front or rear) contacts--since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. As a consequence, device implementation of such films as window layers--without degraded carrier collection--demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions. [ABSTRACT FROM AUTHOR]

Large‐scale manufacturing of polysilicon‐based passivating contacts for high‐efficiency crystalline silicon (c‐Si) solar cells demands simple fabrication of thermally stable SiOx films with well controlled microstructure and nanoscale thickness to enable quantum‐mechanical tunneling. Here, plasma‐dissociated CO2 is investigated to grow in situ thin (<2 nm) SiOx films on c‐Si wafers as tunnel‐oxides for plasma‐deposited, hole‐collecting (i.e., p‐type) polysilicon contacts. It is found that such plasma processing offers excellent thickness control and superior structural integrity upon thermal annealing at 1000 °C, compared to state‐of‐the‐art wet‐chemical oxides. As a result, p‐type polysilicon contacts are achieved on n‐type c‐Si wafers that combine excellent surface passivation, resulting in an implied open‐circuit voltage exceeding 700 mV, with a contact resistance as low as 0.02 Ω cm2. [ABSTRACT FROM AUTHOR]

Passivating contacts consisting of doped polycrystalline silicon (poly‐Si) on a thin tunnel‐oxide enable excellent operating voltages for crystalline silicon solar cells. However, hole‐collecting contacts based on boron‐doped poly‐Si do not yet reach their full surface‐passivation potential, likely due to boron diffusion during annealing. In this work, the authors show how the insertion of a thin intrinsic silicon buffer layer between the silicon oxide and poly‐Si is effective in improving the contact passivation. By tailoring the microstructure of the buffer layer, the chemical passivation and contact resistivity are simultaneously significantly improved. On device level, the buffer layer enables a ≈30 mV open‐circuit voltage enhancement and 1.4% absolute gain in power conversion efficiency. [ABSTRACT FROM AUTHOR]

Doped hydrogenated amorphous silicon (a-Si:H) films of only a few nanometer thin find application in a-Si:H/crystalline silicon heterojunction solar cells. Although such films may yield a field effect at the interface, their electronic passivation properties are often found to be inferior, compared to those of their intrinsic counterparts. In this article, based on H2 effusion experiments, the authors argue that this phenomenon is caused by Fermi energy dependent Si¿H bond rupture in the a-Si:H films, for either type of doping. This results in the creation of Si dangling bonds, counteracting intentional doping of the a-Si:H matrix, and lowering the passivation quality. [ABSTRACT FROM AUTHOR]

In amorphous/crystalline silicon heterojunction solar cells, an inversion layer is present at the front interface. By combining numerical simulations and experiments, we examine the contribution of the inversion layer to lateral transport and assess whether this layer can be exploited to replace the front transparent conductive oxide (TCO) in devices. For this, heterojunction solar cells of different areas (2 × 2, 4 × 4, and 6 × 6 mm2) with and without TCO layers on the front side were prepared. Laser-beam-induced current measurements are compared with simulation results from the ASPIN2 semiconductor simulator. Current collection is constant across millimeter distances for cells with TCO; however, carriers traveling more than a few hundred microns in cells without TCO recombine before they can be collected. Simulations show that increasing the valence band offset increases the concentration of holes under the surface of n-type crystalline silicon, which increases the conductivity of the inversion layer. Unfortunately, this also impedes transport across the barrier to the emitter. We conclude that the lateral conductivity of the inversion layer may not suffice to fully replace the front TCO in heterojunction devices. [ABSTRACT FROM AUTHOR]

Silicon heterojunction solar cells have record-high open-circuit voltages but suffer from reduced short-circuit currents due in large part to parasitic absorption in the amorphous silicon, transparent conductive oxide (TCO), and metal layers. We previously identified and quantified visible and ultraviolet parasitic absorption in heterojunctions; here, we extend the analysis to infrared light in heterojunction solar cells with efficiencies exceeding 20%. An extensive experimental investigation of the TCO layers indicates that the rear layer serves as a crucial electrical contact between amorphous silicon and the metal reflector. If very transparent and at least 150 nm thick, the rear TCO layer also maximizes infrared response. An optical model that combines a ray-tracing algorithm and a thin-film simulator reveals why: parallel-polarized light arriving at the rear surface at oblique incidence excites surface plasmons in the metal reflector, and this parasitic absorption in the metal can exceed the absorption in the TCO layer itself. Thick TCO layers-or dielectric layers, in rear-passivated diffused-junction silicon solar cells-reduce the penetration of the evanescent waves to the metal, thereby increasing internal reflectance at the rear surface. With an optimized rear TCO layer, the front TCO dominates the infrared losses in heterojunction solar cells. As its thickness and carrier density are constrained by anti-reflection and lateral conduction requirements, the front TCO can be improved only by increasing its electron mobility. Cell results attest to the power of TCO optimization: With a high-mobility front TCO and a 150-nm-thick, highly transparent rear ITO layer, we recently reported a 4-cm2 silicon heterojunction solar cell with an active-area short-circuit current density of nearly 39 mA/cm2 and a certified efficiency of over 22%. [ABSTRACT FROM AUTHOR]

Excellent amorphous/crystalline silicon interface passivation is of extreme importance for high-efficiency silicon heterojunction solar cells. This can be obtained by inserting hydrogen-plasma treatments during deposition of the amorphous silicon passivation layers. Prolonged hydrogen-plasmas lead to film etching. We report on the defect creation induced by such treatments: A severe drop in interface-passivation quality is observed when films are etched to a thickness of less than 8 nm. Detailed characterization shows that this decay is due to persistent defects created at the crystalline silicon surface. Pristine interfaces are preserved when the post-etching film thickness exceeds 8 nm, yielding high quality interface passivation. [ABSTRACT FROM AUTHOR]

The article focuses on the progress of perovskite/silicon tandem solar cells towards commercialization, highlighting advances in laboratory-scale performance, various device configurations, and the challenges of scaling up the manufacturing process. It emphasizes the need for improving stability, addressing material and sustainability considerations, and conducting rigorous testing to ensure the commercial viability and bankability of perovskite/silicon tandem technologies.