Ligand Homogenized Br-I Wide-Bandgap Perovskites for Efficient NiOx-Based Inverted Semitransparent and Tandem Solar Cells.

Phase heterogeneity of bromine-iodine (Br-I) mixed wide-bandgap (WBG) perovskites has detrimental effects on solar cell performance and stability. Here, we report a heterointerface anchoring strategy to homogenize the Br-I distribution and mitigate the segregation of Br-rich WBG-perovskite phases. We find that methoxy-substituted phenyl ethylammonium (x-MeOPEA+) ligands not only contribute to the crystal growth with vertical orientation but also promote halide homogenization and defect passivation near the buried perovskite/hole transport layer (HTL) interface as well as reduce trap-mediated recombination. Based on improvements in WBG-perovskite homogeneity and heterointerface contacts, NiOx-based opaque WBG-perovskite solar cells (WBG-PSCs) achieved impressive open-circuit voltage (Voc) and fill factor (FF) values of 1.22 V and 83%, respectively. Moreover, semitransparent WBG-PSCs exhibit a PCE of 18.5% (15.4% for the IZO front side) and a high FF of 80.7% (79.4% for the IZO front side) for a designated illumination area (da) of 0.12 cm2. Such a strategy further enables 24.3%-efficient two-terminal perovskite/silicon (double-polished) tandem solar cells (da of 1.159 cm2) with a high Voc of over 1.90 V. The tandem devices also show high operational stability over 1000 h during T90 lifetime measurements.

Insights into the Si─H Bonding Configuration at the Amorphous/Crystalline Silicon Interface of Silicon Heterojunction Solar Cells by Raman and FTIR Spectroscopy.

In silicon heterojunction solar cell technology, thin layers of hydrogenated amorphous silicon (a-Si:H) are applied as passivating contacts to the crystalline silicon (c-Si) wafer. Thus, the properties of the a-Si:H is crucial for the performance of the solar cells. One important property of a-Si:H is its microstructure which can be characterized by the microstructure parameter R based on Si─H bond stretching vibrations. A common method to determine R is Fourier transform infrared (FTIR) absorption measurement which, however, is difficult to perform on solar cells for various reasons like the use of textured Si wafers and the presence of conducting oxide contact layers. Here, it is demonstrated that Raman spectroscopy is suitable to determine the microstructure of bulk a-Si:H layers of 10 nm or less on textured c-Si underneath indium tin oxide as conducting oxide. A detailed comparison of FTIR and Raman spectra is performed and significant differences in the microstructure parameter are obtained by both methods with decreasing a-Si:H film thickness.

Impermeable Atomic Layer Deposition for Sputtering Buffer Layer in Efficient Semi-Transparent and Tandem Solar Cells via Activating Unreactive Substrate.

Atomic layer deposition (ALD) turns out to be particularly attractive technology for the sputtering buffer layer when preparing the semi-transparent (ST) perovskite solar cells (PSCs) and the tandem solar cells. ALD process turns to be island growth when the substrate is unreactive with the ALD reactants, resulting in the pin-hole layer, which causes an adverse effect on anti-sputtering. Here, p-i-n structured PSCs with ALD SnOx as sputtering buffer layer are conducted. The commonly used electron transportation layer (ETL) PCBM in the p-i-n structured PVK solar cell is an unreactive substrate that prevents the layer-by-layer growth for the ALD SnOx . PCBM layer is activated by introducing reaction sites to form impermeable ALD layers. By introducing reaction sites/ALD SnOx as sputtering buffer layer, the authors succeed to fabricate ST-PSCs and perovskite/silicon (double-side polished) tandem solar cells with power conversion efficiency (PCE) of 20.25% and 23.31%, respectively. Besides, the unencapsulated device with reaction sites maintains more than 99% of the initial PCE after aging over 5100 h. This work opens a promising avenue to prepare impermeable layer for stable PSCs, ST-PSCs, tandem solar cells, and the related scale-up solar cells.

Strain Modulation for Light-Stable n-i-p Perovskite/Silicon Tandem Solar Cells.

Perovskite/silicon tandem solar cells are promising to penetrate photovoltaic market. However, the wide-bandgap perovskite absorbers used in top-cell often suffer severe phase segregation under illumination, which restricts the operation lifetime of tandem solar cells. Here, a strain modulation strategy to fabricate light-stable perovskite/silicon tandem solar cells is reported. By employing adenosine triphosphate, the residual tensile strain in the wide-bandgap perovskite absorber is successfully converted to compressive strain, which mitigates light-induced ion migration and phase segregation. Based on the wide-bandgap perovskite with compressive strain, single-junction solar cells with the n-i-p layout yield a power conversion efficiency (PCE) of 20.53% with the smallest voltage deficits of 440 mV. These cells also maintain 83.60% of initial PCE after 2500 h operation at the maximum power point. Finally, these top cells are integrated with silicon bottom cells in a monolithic tandem device, which achieves a PCE of 26.95% and improved light stability at open-circuit.

Stable Organic Passivated Carbon Nanotube-Silicon Solar Cells with an Efficiency of 22.

The organic passivated carbon nanotube (CNT)/silicon (Si) solar cell is a new type of low-cost, high-efficiency solar cell, with challenges concerning the stability of the organic layer used for passivation. In this work, the stability of the organic layer is studied with respect to the internal and external (humidity) water content and additionally long-term stability for low moisture environments. It is found that the organic passivated CNT/Si complex interface is not stable, despite both the organic passivation layer and CNTs being stable on their own and is due to the CNTs providing an additional path for water molecules to the interface. With the use of a simple encapsulation, a record power conversion efficiency of 22% is achieved and a stable photovoltaic performance is demonstrated. This work provides a new direction for the development of high-performance/low-cost photovoltaics in the future and will stimulate the use of nanotubes materials for solar cells applications.

Phosphorus Catalytic Doping on Intrinsic Silicon Thin Films for the Application in Silicon Heterojunction Solar Cells.

Parasitic absorption and limited fill factor (FF) brought in by the use of amorphous silicon layers are efficiency-limiting challenges for the silicon heterojunction (SHJ) solar cells. In this work, postdeposition phosphorus (P) catalytic doping (Cat-doping) on intrinsic amorphous silicon (a-Si:H(i)) at a low substrate temperature was carried out and a P concentration of up to 6 × 1021 cm-3 was reached. The influences of filament temperature, substrate temperature, and processing pressure on the P profiles were systemically studied by secondary-ion mass spectrometry. By replacing the a-Si:H(n+er with P Cat-doping of an a-Si:H(i) layer, the passivation quality was improved, reaching an iVOC of 741 mV, while the parasitic absorption was reduced, leading to an increase in JSC by ∼1 mA/cm2. On the other hand, the open-circuit voltage and the FF of a conventional SHJ solar cell (with the a-Si:H(n) layer) can be improved by adding a Cat-doping process on the a-Si:H(i) layer, resulting in an increase in FF by 4.7%abs and in efficiency by 1.5%abs.

Development of Conductive SiCx:H as a New Hydrogenation Technique for Tunnel Oxide Passivating Contacts.

Conductive hydrogenated silicon carbide (SiCx:H) is discovered as a promising hydrogenation material for tunnel oxide passivating contacts (TOPCon) solar cells. The proposed SiCx:H layer enables a good passivation quality and features a good electrical conductivity, which eliminates the need of etching back of SiNx:H and indium tin oxide (ITO)/Ag deposition for metallization and reduces the number of process steps. The SiCx:H is deposited by hot wire chemical vapor deposition (HWCVD) and the filament temperature (Tf) during deposition is systematically investigated. Via tuning the SiCx:H layer, implied open-circuit voltages (iVoc) up to 742 ± 0.5 mV and a contact resistivity (ρc) of 21.1 ± 5.4 mΩ·cm2 is achieved using SiCx:H on top of poly-Si(n)/SiOx/c-Si(n) stack at Tf of 2000 °C. Electrochemical capacitance-voltage (ECV) and secondary ion mass spectrometry (SIMS) measurements were conducted to investigate the passivation mechanism. Results show that the hydrogenation at the SiOx/c-Si(n) interface is responsible for the high passivation quality. To assess its validity, the TOPCon stack was incorporated as rear electron selective-contact in a proof-of-concept n-type solar cells featuring ITO/a-Si:H(p)/a-Si:H(i) as front hole selective-contact, which demonstrates a conversion efficiency up to 21.4%, a noticeable open-circuit voltage (Voc) of 724 mV and a fill factor (FF) of 80%.

Ultra-Thin Monocrystalline Silicon Solar Cell with 12.2% Efficiency Using Silicon-On-Insulator Substrate.

Single side heterojunction silicon solar cells were designed and fabricated using Silicon-On-Insulator (SOI) substrate. The TCAD software was used to simulate the effect of silicon layer thickness, doping concentration and the series resistance. A 10.5 µm thick monocrystalline silicon layer was epitaxially grown on the SOI with boron doping concentration of 2 x 10(16) cm(-3) by thermal CVD. Very high Voc of 678 mV was achieved by applying amorphous silicon heterojunction emitter on the front surface. The single cell efficiency of 12.2% was achieved without any light trapping structures. The rear surface recombination and the series resistance are the main limiting factors for the cell efficiency in addition to the c-Si thickness. By integrating an efficient light trapping scheme and further optimizing fabrication process, higher efficiency of 14.0% is expected for this type of cells. It can be applied to integrated circuits on a monolithic chip to meet the requirements of energy autonomous systems.