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%.

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Hydrogenated nanocrystalline silicon oxide (nc‐SiOx:H) layers exhibit promising optoelectrical properties for carrier‐selective‐contacts in silicon heterojunction (SHJ) solar cells. However, achieving high conductivity while preserving crystalline silicon (c‐Si) passivation quality is technologically challenging for growing thin layers (less than 20 nm) on the intrinsic hydrogenated amorphous silicon ((i)a‐Si:H) layer. Here, we present an evaluation of different strategies to improve optoelectrical parameters of SHJ contact stacks founded on highly transparent nc‐SiOx:H layers. Using plasma‐enhanced chemical vapor deposition, we firstly investigate the evolution of optoelectrical parameters by varying the main deposition conditions to achieve layers with refractive index below 2.2 and dark conductivity above 1.00 S/cm. Afterwards, we assess the electrical properties with the application of different surface treatments before and after doped layer deposition. Noticeably, we drastically improve the dark conductivity from 0.79 to 2.03 S/cm and 0.02 to 0.07 S/cm for n‐ and p‐contact, respectively. We observe that interface treatments after (i)a‐Si:H deposition not only induce prompt nucleation of nanocrystals but also improve c‐Si passivation quality. Accordingly, we demonstrate fill factor improvement of 13.5%abs from 65.6% to 79.1% in front/back‐contacted solar cells. We achieve conversion efficiency of 21.8% and 22.0% for front and rear junction configurations, respectively. The optical effectiveness of contact stacks based on nc‐SiOx:H is demonstrated by averagely 1.5 mA/cm2 higher short‐circuit current density thus nearly 1%abs higher cell efficiency as compared with the (n)a‐Si:H.

We have developed a microcrystalline silicon oxide (μc-SiOx:H) p-type emitter layer that significantly improves the light incoupling at the front side of silicon heterojunction solar cells by minimizing reflection losses. The μc-SiOx:H p-layer with a refractive index of 2.87 at 632 nm wavelength and the transparent conducting oxide form a stack with refractive indexes which consecutively decrease from silicon to the ambient air and thus significantly reduce the reflection. Optical simulations performed for flat wafers reveal that the antireflective effect of the emitter overcompensates the parasitic absorption and suggest an ideal thickness of about 40 nm. On textured wafers, the increase in current density is still more than 1 mA/cm2 for a typical emitter thickness of 10 nm. Thus, we are able to fabricate heterojunction solar cells with current densities significantly over 40 mA/cm2 and power conversion efficiency above 20%, which is yet mainly limited by the cell's fill factor.

We investigated hydrogenated nanocrystalline silicon (nc‐Si:H) films as doped emitter layers for silicon heterojunction solar cells. Firstly, we focused on the effect of the nc‐Si:H deposition conditions and film growth on the intrinsic hydrogenated amorphous silicon passivation layer ((i)a‐Si:H) underneath. Three different p‐doped emitters were compared: nc‐Si:H, nc‐SiOx:H, and a‐Si:H. We found that the nc‐Si:H and nc‐SiOx:H growth enhances the passivation of the epitaxy‐free (i)a‐Si:H layer, yielding implied open circuit voltages above 730 mV. Secondly, for (p)nc‐Si:H emitters, we observed a trade‐off between fill factor (FF) and open circuit voltage (Voc) by using two types of (i)a‐Si:H films. A slight epitaxy of the (i)layer seems to promote the rapid nucleation of nc‐Si:H, thereby positively affecting the FF (79.5%) and series resistance but reducing Voc (670 mV). Contrarily, on well‐passivating (i)a‐Si:H the nc‐Si:H nucleation is more difficult resulting in S‐shaped I–V curves, presumably due to low built‐in voltage and a poor emitter/TCO contact. To circumvent this dilemma, a CO2 plasma treatment is used to oxidize the a‐Si:H surface before the nc‐Si:H emitter deposition thereby enhancing nucleation. Accordingly, a FF of 74.5% with Voc of 727 mV is reached in the best device, yielding a conversion efficiency of 21%. HR‐TEM micrograph of the front layer stack of the solar cell. The image shows a region close to the valley between two pyramids. From bottom to top: c‐Si substrate, (i)a‐Si:H passivation layer showing epitaxially grown regions, (p)nc‐Si:H emitter layer, and In2O3:Sn (ITO). Yellow lines highlight layers and individual crystals. Silicon zone axis orientation is <101>.

We performed optical simulations using hydrogenated nanocrystalline silicon oxide (nc-SiO:H) as n-doped interlayer in monolithic perovskite/c-Si heterojunction tandem solar cells. Depending on the adjustable value of its refractive index (2.0 - 2.7) and thickness, nc-SiO:H allows to optically manage the infrared light absorption in the c-Si bottom cell minimizing reflection losses. We give guidelines for nc-SiO:H optimization in tandem devices in combination with a systematic investigation of the effect of the surface morphology (flat or textured) on the photocurrent density. For full-flat and rear textured devices, we found matched photocurrents higher than 19 and 20 mA/cm, respectively, using a 90 nm nc-SiO:H interlayer with a refractive index of 2.7.

Hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) films have demonstrated a unique combination of low parasitic absorption and high conductivity. Here, we report on the use of n-type nc-SiOx:H as front surface field (FSF) in rear-emitter silicon heterojunction (SHJ) solar cells exhibiting excellent electrical cell parameters at a thickness down to only 5 nm. Using a seed layer, we are able to maintain excellent electrical performance (high fill factor (FF) and open circuit voltage (VOC)), while enhancing layer transparency for maximizing short circuit current (JSC). These results, together with the short deposition time (< 100 s), make the (n)nc-SiOx:H FSF attractive for reducing production costs in industrial applications. The best device, with the optimized (n)nc-SiOx:H FSF layer, shows VOC of 731 mV, FF of 80.6%, JSC of 38.3 mA/cm 2 and a power conversion efficiency of 22.6%.

Silicon heterojunction solar cells (SHJ) have been increasingly attracting attention to the PV community in the last years due to their high efficiency potential and the lean production process. We report on the development of a stable baseline process for SHJ cells with a focus on the optical improvement of the solar cells' front side. An amorphous silicon oxide layer (a-SiO 2 ) was used as an anti-reflective coating (AR) on top of the finished SHJ devices. Both optical simulations and experimental results demonstrate a short circuit current density (J sc ) improvement of 0.4 mA/cm 2 when applying the a-SiO 2 AR, yielding maximum conversion efficiencies of 23.0 %. Full-size cells with 244-cm 2 total area have been produced using three front contact stacks: ITO as reference, ZnO:Al and ZnO:Al/SiO 2 showing the J sc improvement with the double AR configuration. Damp-heat tests on those samples are currently being carried out.