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Monolithic perovskite/silicon tandem solar cells recently surpass the efficiency of silicon single‐junction solar cells. Most tandem cells utilize >250 μm thick, planarized float‐zone (FZ) silicon, which is not compatible with commercial production using <200 μm thick Czochralski (CZ) silicon. The perovskite/silicon tandem cells based on industrially relevant 100 μm thick CZ‐silicon without mechanical planarization are demonstrated. The best power conversion efficiency (PCE) of 27.9% is only marginally below the 28.2% reference value obtained on the commonly used front‐side polished FZ‐Si, which are about three times thicker. With both wafer types showing the same median PCE of 27.8%, the thin CZ‐Si‐based devices are preferred for economic reasons. To investigate perspectives for improved current matching and, therefore, further efficiency improvement, optical simulations with planar and textured silicon have been conducted: the perovskite's bandgap needs to be increased by ≈0.02 eV when reducing the silicon thickness from 280 to 100 μm. The need for bandgap enlargement has a strong impact on future tandem developments ensuring photostable compositions with lossless interfaces at bandgaps around or above 1.7 eV. [ABSTRACT FROM AUTHOR]

Doped hydrogenated nanocrystalline (nc-Si:H) and silicon oxide (nc-SiOx:H) materials grown by plasma-enhanced chemical vapor deposition have favourable optoelectronic properties originated from their two-phase structure. This unique combination of qualities, initially, led to the development of thin-film Si solar cells allowing the fabrication of multijunction devices by tailoring the material bandgap. Furthermore, nanocrystalline silicon films can offer a better carrier transport and field-effect passivation than amorphous Si layers could do, and this can improve the carrier selectivity in silicon heterojunction (SHJ) solar cells. The reduced parasitic absorption, due to the lower absorption coefficient of nc-SiOx:H films in the relevant spectral range, leads to potential gain in short circuit current. In this work, we report on development and applications of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) from material to device level. We address the potential benefits and the challenges for a successful integration in SHJ solar cells. Finally, we prove that nc-SiOx:H demonstrated clear advantages for maximizing the infrared response of c-Si bottom cells in combination with perovskite top cells. [ABSTRACT FROM AUTHOR]

Perovskite/silicon tandem solar cells are attractive for their potential for boosting cell efficiency beyond the crystalline silicon (Si) single‐junction limit. However, the relatively large optical refractive index of Si, in comparison to that of transparent conducting oxides and perovskite absorber layers, results in significant reflection losses at the internal junction between the cells in monolithic (two‐terminal) devices. Therefore, light management is crucial to improve photocurrent absorption in the Si bottom cell. Here it is shown that the infrared reflection losses in tandem cells processed on a flat silicon substrate can be significantly reduced by using an optical interlayer consisting of nanocrystalline silicon oxide. It is demonstrated that 110 nm thick interlayers with a refractive index of 2.6 (at 800 nm) result in 1.4 mA cm−² current gain in the silicon bottom cell. Under AM1.5G irradiation, the champion 1 cm2 perovskite/silicon monolithic tandem cell exhibits a top cell + bottom cell total current density of 38.7 mA cm−2 and a certified stabilized power conversion efficiency of 25.2%. The optical absorption in monolithic perovskite/silicon tandem solar cells with flat Si front‐side is improved. The successful tailoring and incorporation of a nanocrystalline silicon oxide composite interlayer with tuneable refractive index is demonstrated on device by experiments and optical simulations. Improved short‐circuit current density (38.7 mA cm−2) combined with excellent contact properties lead to a cell with a certified stabilized conversion efficiency of 25.2%. [ABSTRACT FROM AUTHOR]

Abstract In this study we make a detailed comparison between indium tin oxide (ITO), aluminum-doped zinc oxide (ZnO:Al) and hydrogenated indium oxide (IO:H) when applied on the illuminated side of rear-junction silicon heterojunction (SHJ) solar cells. ITO being the state of the art material for this application, ZnO:Al being an attractive substitute due to its cost effectiveness and IO:H being a transparent conductive oxide (TCO) with high-mobility and excellent optical properties. Through numerical simulations, the optically optimal thicknesses for a double layer anti-reflective coating system, consisting of the respective TCO and amorphous silicon oxide (a-SiO 2) capping layers are defined. Through two-dimensional electrical simulations, we present a comparison between front-junction and rear-junction devices to show the behavior of series resistance (R s) in dependence of the TCO sheet resistance (R sh) and the device effective lifetime (τ eff). The study indicates that there is a τ eff dependent critical TCO R sh value, above which, the rear-junction device will become advantageous over the front-junction design in terms of R s. Solar cells with the respective layers are analyzed. We show that a thinner TCO optimized layer will result in a benefit in cell performance when implementing a double layer anti-reflective coating. We conclude that for a highest efficiency solar cell performance, a high mobility TCO, like IO:H, is required as the device simulations show. However, the rear-junction solar cell design permits the implementation of a lower conductive TCO in the example of the cost-effective ZnO:Al with comparable performance to the ITO, opening the possibility for substitution in mass production. Highlights • ITO, ZnO:Al and IO:H for SHJ solar cells comparison, simulations and experimental. • Optimized thinner TCO layers for SHJ solar cells improved performance. • Substitution of ITO by ZnO:Al in mass production. [ABSTRACT FROM AUTHOR]

Silicon Heterojunction has become a promising technology to substitute passivated emitter and rear contact (PERC) solar cells in pursuance of lower levelized cost of electricity through high efficiency devices. While high open circuit voltages and fill factors are reached, current loss related to the front and rear contacts, such as the transparent conductive oxide (TCO) layers is still a limiting factor to come closer to the efficiency limit of silicon based solar cells. Furthermore, reducing indium consumption for the TCO has become mandatory to push silicon heterojunction technology towards a terawatt scale production due to material scarcity and costs. To address these issues dielectric layers, such as silicon dioxide or nitride cappings are implemented to reduce TCO thicknesses both diminishing parasitic absorption and material consumption. However, reducing the TCO thickness comes in cost of resistive losses. Furthermore, the TCO properties do vary with thickness and neighboring layer configuration altering the optimization frame of the device. In this paper we present a detailed analysis to quantify the optoelectrical losses trade-off associated to the TCO thickness reduction in such layer stacks. Through the analysis we show and explain why experimental bifacial cells with 20 nm front and rear TCO perform at a similar level to reference cells with 75 nm under front and rear illumination reaching efficiency close to 24% at 92% bifaciality. We present as well a simple interconnection method via screen printing metallization to implement a thin TCO/silicon dioxide/silver reflector enhancing current density from 39.6 to 40.4 mA/cm2 without compromising resistive losses resulting in a 0.2% absolute solar cell efficiency increase from a bifacial design (23.5–23.7%). Finally, following this approach we present a certified champion cell with an efficiency of 24.6%. • Analysis of TCO variations on electron and hole contact for Si heterojunction solar cells by simulations and experiments. • Both sides 20 nm TCO + SiO 2 layer stack SHJ solar cells with 23.9% efficiency. • Champion solar cell with rear 20 nm TCO + SiO 2 layer stack and silver rear reflector with 24.6% efficiency. [ABSTRACT FROM AUTHOR]