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Excellent surface passivation induced by (i)a‐Si:H is critical to achieve high‐efficiency silicon heterojunction (SHJ) solar cells. This is key for conventional single‐junction cell applications but also for bottom cell application in tandem devices. In this study, we investigated the effects of (i)a‐Si:H deposition temperature on passivation quality and SHJ solar cell performance. At the lower end of temperatures ranging from 140°C to 200°C, it was observed with Fourier‐transform infrared spectroscopy (FTIR) that (i)a‐Si:H films are less dense, thus hindering their surface passivation capabilities. However, with additional hydrogen plasma treatments (HPTs), those (i)a‐Si:H layers deposited at lower temperatures exhibited significant improvements and better passivation qualities than their counterparts deposited at higher temperatures. On the other hand, even though we observed the highest VOCs for cells with (i)a‐Si:H deposited at the lowest temperature (140°C), the related FFs are poorer as compared to their higher temperature counterparts. The optimum trade‐off between VOC and FF for the SHJ cells was found with temperatures ranging from 160°C to 180°C, which delivered independently certified efficiencies of 23.71%. With a further improved p‐layer that enables a FF of 83.3%, an efficiency of 24.18% was achieved. Thus, our study reveals two critical requirements for optimizing the (i)a‐Si:H layers in high‐efficiency SHJ solar cells: (i) excellent surface passivation quality to reduce losses induced by interface recombination and simultaneously (ii) less‐defective (i)a‐Si:H bulk to not disrupt the charge carrier collections. [ABSTRACT FROM AUTHOR]

Solar cells based on black silicon (b‐Si) are proven to be promising in photovoltaics (PVs) by exceeding 22% efficiency. To reach high efficiencies with b‐Si surfaces, the most crucial step is the effective surface passivation. Up to now, the highest effective minority carrier lifetimes are achieved with atomic layer‐deposited Al2O3 or thermal SiO2. Plasma‐enhanced chemical vapor deposition (PECVD)‐grown hydrogenated amorphous silicon (a‐Si:H) passivation of b‐Si is seldom reported due to conformality problems. In this current study, b‐Si surfaces superposed on standard pyramidal textures, also known as modulated surface textures (MSTs), are successfully passivated by PECVD‐grown conformal layers of a‐Si:H. It is shown that under proper plasma‐processing conditions, the effective minority carrier lifetimes of samples endowed with front MST and rear standard pyramidal textures can reach up to 2.3 ms. A route to the conformal growth is described and developed by transmission electron microscopic (TEM) images. Passivated MST samples exhibit less than 4% reflection in a wide spectral range from 430 to 1020 nm. [ABSTRACT FROM AUTHOR]

Passivating contacts based on poly-Si have enabled record-high c-Si solar cell efficiencies due to their excellent surface passivation quality and carrier selectivity. The eventual existence of pinholes within the ultra-thin SiO x layer is one of the key factors for carrier collection, beside the tunneling mechanism. However, pinholes are usually believed to have negative impact on the passivation quality of poly-Si passivating contacts. This work studied the influence of the pinhole density on the passivation quality of ion-implanted poly-Si passivating contacts by decoupling the pinhole generation from the dopants diffusion process by means of two annealing steps: (1) a pre -annealing step at high temperature after the intrinsic poly-Si deposition to visualize the formation of pinholes and (2) a post -annealing step for dopants activation/diffusion after ion-implantation. The pinhole density is quantified in the range of 1✕106 to 3✕108 cm2 by the TMAH selective etching approach. The passivation quality is discussed with respect to the pinhole density and the post-annealing thermal budget (TB) for dopants diffusion. The study shows that a moderate pinhole density does not induce doping profile variations that can be detectable by the coarse spatial resolution of ECV measurements. It is surprising that the existence of pinholes in a moderate density within our thickness fixed SiO x layer can effectively enhance the passivation qualities for both n + and p + poly-Si passivating contacts. We speculate the reason is due to the enhanced field-effect passivation at the pinhole surrounding. In fact, the variation of the passivation quality depends on the balance between a strengthened field-effect passivation and an excessive local Auger recombination, being both effects induced by the higher and deeper level of dopants diffused into the c-Si surface through the pinholes. • Decoupling of the pinhole formation and the dopant diffusion using two annealing processes. • Application of the thermal diffusion budget concept to the fabrication of the poly-Si passivating contacts. • The existence of pinholes within the SiO x layer enhances the localized dopant diffusion. • The dopant diffusion through the pinholes enhances the electrical field passivation locally. • A moderate pinhole density within SiO x induces obvious increase in passivation qualities for both n+ and p+ poly-Si passivating contacts, although the sensitivity of passivation on pinhole density is less for p + poly-Si. [ABSTRACT FROM AUTHOR]