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Ultrathin solar cells can be a path forward to low‐cost photovoltaics due to their reduced material consumption and shorter required deposition times. With excellent surface passivation, such devices may feature higher open‐circuit voltages (VOC). However, their short‐circuit current density (JSC) may be reduced due to decreased light absorption. This mandates implementation of efficient light‐trapping structures. To design efficient ultrathin solar cells that combine surface‐passivation and light‐trapping features, accurate 3‐D modeling is necessary. To this end, a novel 3‐D optoelectrical finite‐element model is developed to analyze the performance of ultrathin solar cells. The model is applied to the case of ultrathin (<500 nm) chalcogenide solar cells (copper indium gallium (di) selenide, CIGSe), rear‐passivated with nanostructured Al2O3 to circumvent optical and electrical losses. It is found that such a nanopatterned dielectric passivation scheme enhances broadband light‐trapping with reduced rear‐surface recombination, resulting in an absolute power conversion efficiency enhancement of 3.9%, compared to cells without passivation structure. Overall, the work shows how 3‐D finite element modeling can aid in analyzing and developing new optical and electrical solar cell designs for ultrathin solar cells such as those based on chalcogenides and perovskites. [ABSTRACT FROM AUTHOR]

Sputtered nickel oxide (NiOx) is an attractive hole‐transport layer for efficient, stable, and large‐area p‐i‐n metal‐halide perovskite solar cells (PSCs). However, surface traps and undesirable chemical reactions at the NiOx/perovskite interface are limiting the performance of NiOx‐based PSCs. To address these issues simultaneously, an efficient NiOx/perovskite interface passivation strategy by using an organometallic dye molecule (N719) is reported. This molecule concurrently passivates NiOx and perovskite surface traps, and facilitates charge transport. Consequently, the power conversion efficiency (PCE) of single‐junction p‐i‐n PSCs increases from 17.3% to 20.4% (the highest reported value for sputtered‐NiOx based PSCs). Notably, the N719 molecule self‐anchors and conformally covers NiOx films deposited on complex surfaces. This enables highly efficient textured monolithic p‐i‐n perovskite/silicon tandem solar cells, reaching PCEs up to 26.2% (23.5% without dye passivation) with a high processing yield. The N719 layer also forms a barrier that prevents undesirable chemical reactions at the NiOx/perovskite interface, significantly improving device stability. These findings provide critical insights for improved passivation of the NiOx/perovskite interface, and the fabrication of highly efficient, robust, and large‐area perovskite‐based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Ultrathin layers of hydrogenated amorphous silicon (a‐Si:H), passivating the surface of crystalline silicon (c‐Si), are key enablers for high‐efficiency silicon heterojunction solar cells. In this work, the authors apply highly sensitive attenuated total reflectance Fourier‐transform infrared spectroscopy, combined with carrier‐lifetime measurements and carrier‐lifetime imaging, to resolve several fundamental and technology‐related questions related to the a‐Si:H/c‐Si interface. To gain insight, the a‐Si:H/c‐Si interfacial morphology is intentionally manipulated by applying different surface, annealing and ageing treatments. Changes are observed in the vibrational modes of hydrides (SiHX), oxides (SiHX(SiYOZ)) together with hydroxyl and hydrocarbon surface groups. The effect of unintentional oxidation and contamination is considered as well. Electronic interfacial properties are reviewed and discussed of hydrogen mono‐layer passivation of the c‐Si surface and from the perspectives of a‐Si:H bulk properties. It is found that both models have severe limitations and suggest that a new physical model of the interface, considering both is required. [ABSTRACT FROM AUTHOR]

Defects at the surface and grain boundaries of metal–halide perovskite films lead to performance losses of perovskite solar cells (PSCs). Here, organic cyano‐based π‐conjugated molecules composed of indacenodithieno[3,2‐b]thiophene (IDTT) are reported and it is found that their cyano group can effectively passivate such defects. To achieve a homogeneous distribution, these molecules are dissolved in the antisolvent, used to initiate the perovskite crystallization. It is found that these molecules are self‐anchored at the grain boundaries due to their strong binding to undercoordinated Pb2+. On a device level, this passivation scheme enhances the charge separation and transport at the grain boundaries due to the well‐matched energetic levels between the passivant and the perovskite. Consequently, these benefits contribute directly to the achievement of power conversion efficiencies as high as 21.2%, as well as the improved environmental and thermal stability of the PSCs. The surface treatment provides a new strategy to simultaneously passivate defects and enhance charge extraction/transport at the device interface by manipulating the anchoring groups of the molecules. [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]

Passivating metal/silicon contacts combine low carrier recombination with low contact resistivities, enabled by a low gap state density at their interface. Such contacts find applications in high-efficiency solar cells. We perform first-principles calculations based on density functional theory to investigate the surface defect and metal-induced gap state density of silicon in close contact with metals (Al and Ag). We confirm that surface hydrogenation fully removes surface-defect gap states of (111)-oriented silicon surfaces. However, the metal-induced gap state density increases significantly when metals are closer than 0.5 nm to such surfaces. These results highlight the importance of the tunneling-film thickness in achieving effective passivating-contact formation. [ABSTRACT FROM AUTHOR]

Abstract: The device physics of commercially dominant diffused‐junction silicon solar cells is well understood, allowing sophisticated optimization of this class of devices. Recently, so‐called passivating‐contact solar cell technologies have become prominent, with Kaneka setting the world's silicon solar cell efficiency record of 26.63% using silicon heterojunction contacts in an interdigitated configuration. Although passivating‐contact solar cells are remarkably efficient, their underlying device physics is not yet completely understood, not in the least because they are constructed from diverse materials that may introduce electronic barriers in the current flow. To bridge this gap in understanding, we explore the device physics of passivating contact silicon heterojunction (SHJ) solar cells. Here, we identify the key properties of heterojunctions that affect cell efficiency, analyze the dependence of key heterojunction properties on carrier transport under light and dark conditions, provide a self‐consistent multiprobe approach to extract heterojunction parameters using several characterization techniques (including dark J‐V, light J‐V, C‐V, admittance spectroscopy, and Suns‐Voc), propose design guidelines to address bottlenecks in energy production in SHJ cells, and develop a process‐to‐module modeling framework to establish the module's performance limits. We expect that our proposed guidelines resulting from this multiscale and self‐consistent framework will improve the performance of future SHJ cells as well as other passivating contact‐based solar cells. [ABSTRACT FROM AUTHOR]

Silicon heterojunction solar cells use crystalline silicon ( c -Si) wafers as optical absorbers and employ bilayers of doped/intrinsic hydrogenated amorphous silicon ( a -Si:H) to form passivating contacts. Recently, we demonstrated that such solar cells increase their operating voltages and thus their conversion efficiencies during light exposure. We found that this performance increase is due to improved passivation of the a -Si:H/ c -Si interface and is induced by injected charge carriers (either by light soaking or forward-voltage biasing of the device). Here, we discuss this counterintuitive behavior and establish that: (i) the performance increase is observed in solar cells as well as modules; (ii) this phenomenon requires the presence of doped a -Si:H films, but is independent from whether light is incident from the a -Si:H( p ) or the a -Si:H( n ) side; (iii) UV and blue photons do not play a role in this effect; (iv) the performance increase can be observed under illumination intensities as low as 20 W m −1 (0.02-sun) and appears to be almost identical in strength when under 1-sun (1000 W m −1 ); (v) the underlying physical mechanism likely differs from annealing-induced surface passivation. [ABSTRACT FROM AUTHOR]

Bilayers of intrinsic and doped hydrogenated amorphous silicon, deposited on crystalline silicon (c-Si) surfaces, simultaneously provide contact passivation and carrier collection in silicon heterojunction solar cells. Recently, we have shown that the presence of overlaying transparent conductive oxides can significantly affect the c-Si surface potential induced by these amorphous silicon stacks. Specifically, deposition on the hole-collecting bilayers can result in an undesired weakening of contact passivation, thereby lowering the achievable fill factor in a finished device. We test here a variety of organic semiconductors of different doping levels, overlaying hydrogenated amorphous silicon layers and silicon-based hole collectors, to mitigate this effect. We find that these materials enhance the c-Si surface potential, leading to increased implied fill factors. This opens opportunities for improved device performance. [ABSTRACT FROM AUTHOR]

Damage of the hydrogenated amorphous/crystalline silicon interface passivation during transparent conductive oxide sputtering is reported. This occurs in the fabrication process of silicon heterojunction solar cells. We observe that this damage is at least partially caused by luminescence of the sputter plasma. Following low-temperature annealing, the electronic interface properties are recovered. However, the silicon-hydrogen configuration of the amorphous silicon film is permanently changed, as observed from infra-red absorbance spectra. In silicon heterojunction solar cells, although the as-deposited film's microstructure cannot be restored after sputtering, no significant losses are observed in their open-circuit voltage. [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]

We report and explain the photoluminescence (PL) spectra from crystalline silicon (c-Si) wafers passivated by hydrogenated amorphous silicon (a-Si:H) films under various measurement conditions, utilizing the different absorption coefficients and radiative recombination mechanisms in c-Si and a-Si:H. By comparison with the luminescence properties of a-Si:H, we also demonstrate that SiN x films deposited under certain silicon-rich conditions yield luminescence spectra similar to those of a-Si:H, indicating the presence of an a-Si:H-like phase in the SiN x films. This causes a reduction in the blue response of the solar cells via parasitic absorption. In addition, with the ability to detect the specific emission from heavily-doped silicon via band-gap narrowing effects, we can unambiguously separate individual spectral PL signatures of three different layers in a single substrate: the SiN x passivation films, the diffused layers, and the underlying c-Si substrate. Finally, we apply this technique to evaluate parasitic absorption in the passivation films, and the doping density of the diffused layers on different finished solar cells, highlighting the value of this nondestructive contactless, micron-scale technique for photovoltaic applications. [ABSTRACT FROM AUTHOR]