Passivating contacts based on transition metal oxides (TMOs) have the potential to overcome existing performance limitations in high‐efficiency crystalline silicon (c‐Si) solar cells, which is a significant driver for continuing cost/Watt reductions of photovoltaic electricity. Herein, innovative stacks of Al‐alloyed TiO x (Al y TiO x ) and pure TiO x as transparent electron‐selective passivating contacts for n‐type c‐Si surfaces are explored. An optimized stack of 2 nm Al y TiO x and 2 nm TiO x is shown to provide both record‐quality surface passivation and excellent electrical contact, with a surface recombination current density prefactor J 0 of 2.4 fA cm−2 and a specific contact resistivity ρ c of 15.2 mΩ cm2. The performance of this innovative stack significantly exceeds previously reported values for pure or doped TiO x single layers, SiO x /TiO x stacks, a‐Si:H/TiO x stacks, and other transparent contact technologies. Furthermore, an excellent efficiency of 21.9% is attained by incorporating the optimized stack as a full‐area rear contact in an n‐type c‐Si solar cell. The findings set a new benchmark for the passivation performance of metal oxide‐based passivating contacts, bringing it to a level on par with state‐of‐the‐art SiO x /poly‐Si contacts while greatly improving optical transparency.

To reduce the cost of solar photovoltaic electricity generation by overcoming current performance limitations in crystalline silicon (c-Si) solar cells, it is essential to switch from current silicon-based materials to more transparent materials as carrier-selective passivating contacts (CSPCs). Ideal CSPCs should perform three functions simultaneously: they should 1) passivate the silicon dangling bonds in order to provide low surface recombination current density prefactor J 0 (≤10 fA cm −2 ) which ensures high open-circuit voltages at a cell level; 2) operate as efficient contacts for either electrons or holes, with low contact resistivity (≤100 mΩ cm 2 ) to allow high fill factors; and 3) should be highly transparent in the wavelength range corresponding to the solar spectrum in order to reduce parasitic optical losses and hence enable high short-circuit current densities, particularly when applied to the front (illuminated) side of devices. In order to enable practical applications, they should also be thermally stable and prepared using earth-abundant materials. Multiple recent review articles have provided an overview of the development of passivating contact technology in silicon solar cells, testifying to the great interest in this topic. [1] Among passivating contact technologies, those based on hydrogenated amorphous Si (a-Si:H) and polycrystalline Si (poly-Si) layers represent the current state-ofthe-art, having enabled multiple silicon solar cells with worldrecord efficiencies in recent years. [2] However, these materials suffer from significant parasitic optical absorption, which imposes a limit on their ability to provide further improvements in device performance.Transition metal oxides (TMOs) are the leading candidate to replace Si-based materials as CSPCs in order to overcome these limitations. TMOs are very versatile since they can be utilized as both hole-selective contacts, such as MoO x , [3] VO x , [4] and WO x , [5] and electron-selective contacts, such as TiO 2 and ZnO. This is due to the fact that their work functions span a wide range from 3 to 7 eV. [6] Furthermore, TMOs are inexpensive, nontoxic, based on earth-abundant materials, compatible Passivating contact technologies are essential for fabricating high-efficiency crystalline silicon (c-Si) solar cells, and their application and incorporation into manufacturing lines has ranked as a hot topic of research. Generally, ideal passivating contacts should combine excellent electrical contact, outstanding surface passivation, and high optical transparency. However, addressing all these criteria concurrently is challenging since it is unlikely for any single material to exhibit both efficient carrier transport and surface-defect passivation while demonstrating negligible parasitic absorption. In this work, several earth-abundant, wide-bandgap materials are combined to engineer highquality transparent electron-selective passivating contact structures capable of overcoming these obstacles. A highly transparent Al y TiO x /ZnO/TiO 2 stack...

One of the important factors in the performance of perovskite solar cells (PSCs) is effective defect passivation. Dimensional engineering technique is a promising method to efficiently passivate non‐radiative recombination pathways in the bulk and surface of PSCs. Herein, a passivation approach for the perovskite/hole transport layer interface is presented, using a mixture of guanidinium and n‐octylammonium cations introduced via GuaBr and n‐OABr. The dual‐cation passivation layer can provide an open‐circuit voltage of 1.21 V with a power conversion efficiency of 23.13%, which is superior to their single cation counterparts. The mixed‐cation passivation layer forms a 1D/2D perovskite film on top of 3D perovskite, leading to a more hydrophobic and smoother surface than the uncoated film. A smooth surface can diminish non‐radiative recombination and enhance charge extraction at the interface making a better contact with the transport layer, resulting in improved short‐circuit current. In addition, space charge‐limited current measurements show a three times reduction in the trap‐filled limit voltage in the mixed‐cation passivated sample compared with unpassivated cells, indicating fewer trapped states. The shelf‐life stability test in ambient atmosphere with 60% relative humidity as well as light‐soaking stability reveal the highest stability for the dual‐cation surface passivation.

III–V semiconductors are among the highest performing materials for solar energy conversion devices. Exposing III–V semiconductors to a hydrogen plasma can improve optoelectronic properties and is a critical step in fabricating efficient InP solar cells. However, there is a limited understanding of the changes induced by hydrogen plasma exposure to the surface and in the bulk of III–V semiconductors. Herein, it is demonstrated that a 19.3% efficient p‐InP solar cell with a TiO2 electron selective contact layer can be achieved by exposing the InP substrate to hydrogen plasma. Detailed investigations employing ultraviolet photoelectron spectroscopy and capacitance–voltage measurement unveil that the hydrogen plasma exposure on p‐InP leads to charge carrier polarity inversion in the near‐surface region (charge inversion layer) while simultaneously reducing the carrier concentration (charge‐depleted layer) in the bulk. The study provides important insights into the impact of hydrogen plasma exposures on InP which may lead to more efficient optoelectronic devices such as solar cells, photodetectors, light‐emitting diodes, and photoelectrochemical cells.

Surface passivation is crucial for many high-performance solid-state devices, especially solar cells. It has been proposed that 2D hexagonal boron nitride (hBN) films can provide near-ideal passivation due to their wide bandgap, lack of dangling bonds, high dielectric constant, and easy transferability to a range of substrates without disturbing their bulk properties. However, so far, the passivation of hBN has been studied for small areas, mainly because of its small sizes. Here, we report the passivation characteristics of wafer-scale, few monolayers thick, hBN grown by metalorganic chemical vapor deposition. Using a recently reported ITO/i-InP/p+-InP solar cell structure, we show a significant improvement in solar cell performance utilizing a few monolayers of hBN as the passivation layer. Interface defect density (at the hBN/i-InP) calculated using C–V measurement was 2 × 1012 eV−1cm−2 and was found comparable to several previously reported passivation layers. Thus, hBN may, in the future, be a possible candidate to achieve high-quality passivation. hBN-based passivation layers can mainly be useful in cases where the growth of lattice-matched passivation layers is complicated, as in the case of thin-film vapor–liquid–solid and close-spaced vapor transport-based III–V semiconductor growth techniques.

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