Atomic layer deposition of NiO applied in a monolithic perovskite/PERC tandem cell

Nga Phung, Dong Zhang (Corresponding author), Cristian A.A. van Helvoirt, Michael Verhage, Marcel A. Verheijen, V. Zardetto, Frennie Bens, Christ H.L. Weijtens, Bart L.J. Geerligs, W.M.M. Kessels, Bart Macco, M. Creatore (Corresponding author)

Research output: Contribution to journalArticleAcademicpeer-review

4 Citations (Scopus)
115 Downloads (Pure)

Abstract

Monolithic perovskite/silicon tandem photovoltaics have fueled major research efforts as well as gaining rapid industrial interest. So far, most of the literature has focused on the use of currently more expensive silicon
heterojunction bottom cell technology. This work demonstrates a perovskite/silicon tandem solar cell based on the industrially dominant passivated emitter and rear cell (PERC) technology. In detail, we investigate a tunnel recombination junction (TRJ) consisting of ITO/NiO/2-(9H-carbazol-9-yl)ethyl] phosphonic acid (2PACz) and compare it with an ITO/2PACz TRJ. Specifically, the NiO layer is deposited by atomic layer deposition (ALD).
Although ITO/2PACz-based tandem devices can reach more than 24% conversion efficiency, we observe that they suffer from a large spread in photovoltaic parameters due to electrical shunts in the perovskite top cell, caused by the inhomogeneity of the 2PACz layer on ITO. Instead, when ALD NiO is sandwiched between 2PACz and ITO, the surface coverage of 2PACz improves and the yield of the devices, in terms of all device parameters, also improves, i.e., the standard deviation decreases from 4.6% with ITO/2PACz to 2.0% with ITO/NiO/2PACz.
In conclusion, thanks to the presence of NiO, the TRJ consisting of ITO/NiO/2PACz leads to a 23.7% efficient tandem device with narrow device efficiency distribution.
Original languageEnglish
Article number112498
Number of pages8
JournalSolar Energy Materials and Solar Cells
Volume261
DOIs
Publication statusPublished - 1 Oct 2023

Funding

The authors acknowledge the technical support of Caspar van Bommel, Joris Meulendijks and Janneke Zeebregts at TU/e. The authors thank Dr. Beatriz Barcones Campo (TU/e) for preparing the TEM sample using FIB, and Dr. Wim Arnold-Bik at DIFFER for performing RBS measurement. The authors thank Bruno Pinto Branco (TU/e) with the perovskite deposition. Solliance and the Dutch province of Noord-Brabant are acknowledged for funding the TEM facility. This work is supported by the Top consortia for Knowledge and Innovation (TKI) Solar Energy program “PERCspective” ( TEUE119005 ) of the Ministry of Economic Affairs of The Netherlands . M.C. acknowledges the NWO Aspasia program. The improvement in device yield in the presence of NiO could be attributed to the quality of the HTL/perovskite interface or difference in perovskite formation on two TRJs. Therefore, we investigated the perovskite layers grown on ITO/SAM and ITO/NiO/SAM. We adopted scanning electron microscopy (SEM) and X-ray diffraction (XRD) to investigate the morphology of the perovskite layers deposited on ITO/SAM and ITO/NiO/SAM, as shown in Fig. S15 (in section 3 of the Supporting Information). The SEM analysis of Figs. S15a–b shows no relevant difference in terms of grain size distribution in the perovskite when grown on ITO/SAM and ITO/NiO/SAM (Figs. S15c–d). Interestingly, Li et al. also reported a large number of shunted cells when using only SAM on flexible ITO substrates in all perovskite tandem devices. In contrast, using NiO/SAM significantly improved the device yield, where NiO layer is fabricated by solution-processing from nanoparticles [34]. They attributed this improvement to better wetting of perovskite solution on ITO/NiO/SAM, which delivered a compact perovskite layer, unlike a perovskite film with pinholes, when processed directly on ITO/SAM. Although the improvement in device yield is similar to our case, the SEM image in Fig. S15a shows that the perovskite layer on ITO/SAM is compact without pinholes, ruling out the difference in perovskite coverage in this study. In addition, Figs. S15e–f reports the XRD patterns of the perovskite layers: there is only a negligible difference in the perovskite crystallographic structure when the absorber is grown on NiO/SAM or on SAM. Hence, we can conclude that the improvement in device yield upon introduction of NiO in the TRJ cannot be attributed to the perovskite microstructure and crystallographic properties.We then hypothesize that the electrical shunts in the top cell when adopting ITO/SAM as TRJ, as addressed in relation to Fig. 2c and d, are caused by an inhomogeneous distribution of 2PACz on ITO. This has been already observed in perovskite single junction using plasma-assisted ALD NiO [27] and sputtered NiO [35] in combination with phosphonic acid SAM. To verify this hypothesis, we carry out electrostatic force microscopy (EFM) measurements on the ITO/SAM surface. Fig. 4 presents the contact potential difference (CPD) map of the ITO/SAM. The CPD between the EFM tip and the surface represents the difference in work function between the tip and the material underneath. Thus, it is possible to rely on the relative change in CPD mapping to investigate the homogeneity of the SAM. This is because the work function of 2PACz is 5.2 eV, whereas the work function of the employed ITO is 4.0 eV, and the work function of ALD NiO is 4.3 eV, as measured by ultraviolet photoelectron spectroscopy (see Method for details). As can be seen in Fig. 4a and b, the map shows variation in CPD of the SAM layer deposited on ITO, which is different from the homogeneous CPD of ITO without SAM, despite similar morphology features (height map of ITO and ITO/SAM can be found in Fig. S16, Supporting Information). There are several spots on the map in Fig. 4a showing lower CPD than the rest of the surface of the sample. These low CPD spots likely correspond to exposed ITO areas, as the work function of the ITO is lower than the work function of SAM. It is plausible that the different densities of these spots lead to the difference in perovskite top cell performance, resulting in a large device performance variation seen in Fig. 2c and d. In contrast, when NiO is introduced in the TRJ, the CPD map shows no significant local variation (Fig. 4c), suggesting homogeneous SAM formation and corroborating the TEM results. We attribute this difference in SAM distribution on ITO and ITO/NiO to the higher hydroxyl group density on the NiO surface with respect to pristine ITO, as shown by XPS. The XPS analysis of O1s spectra on ITO/NiO and ITO surfaces in Figs. S4 and S5 (Supporting information) indicates that the NiO surface is characterized by a higher ratio of hydroxyl bonds to metal oxide bonds (-OH/O2− = 0.66±0.07) than the pristine ITO surface (-OH/O2− = 0.43±0.04). A similar observation has been reported for SAM directly deposited on different ITO layers, where ITO layers with a higher hydroxyl concentration result in non-shunted single junction device, whereas sputtered ITO in a monolithic perovskite/SHJ tandem with low -OH concentration results in shunted top cells and thereby non-working tandem cells [36]. Note that the ITO/SAM and ITO/NiO/SAM have similar roughness of 46 and 44 nm, respectively, as extracted from atomic force microscopy height maps in Fig. S16 (Supporting information). This indicates that roughness is not the cause for the difference seen in device efficiency distributions utilizing ITO/SAM or ITO/NiO/SAM.The authors acknowledge the technical support of Caspar van Bommel, Joris Meulendijks and Janneke Zeebregts at TU/e. The authors thank Dr. Beatriz Barcones Campo (TU/e) for preparing the TEM sample using FIB, and Dr. Wim Arnold-Bik at DIFFER for performing RBS measurement. The authors thank Bruno Pinto Branco (TU/e) with the perovskite deposition. Solliance and the Dutch province of Noord-Brabant are acknowledged for funding the TEM facility. This work is supported by the Top consortia for Knowledge and Innovation (TKI) Solar Energy program “PERCspective” (TEUE119005) of the Ministry of Economic Affairs of The Netherlands. M.C. acknowledges the NWO Aspasia program.

FundersFunder number
ITO
Top consortia for Knowledge and InnovationTEUE119005
Society for American Music
National Institute of Oceanography, India
Ministerie van Economische Zaken en Klimaat
Nederlandse Organisatie voor Wetenschappelijk Onderzoek

    Keywords

    • Atomic layer deposition
    • Nickel oxide
    • PERC
    • Perovskite/Silicon tandem cell
    • Self-assembled monolayer
    • Tunnel recombination junction

    Fingerprint

    Dive into the research topics of 'Atomic layer deposition of NiO applied in a monolithic perovskite/PERC tandem cell'. Together they form a unique fingerprint.

    Cite this