EU PVSEC Programme Online
EU PVSEC 2020, 7 - 11 September 2020
Presentation: 2BO.3.6 Aiming for Fully Suitable High-Mobility TCOs for Silicon Heterojunction Solar Cells
Type: Oral
Date: Tuesday, 8th September 2020
13:30 - 15:00
Author(s): D. Erfurt, M. Dimer, A. Cruz Bournazou, A.B. Morales-Vilches, E.C. Wang, R. Köhler, U. Graupner, E. Schneiderlöchner, R. Schlatmann, B. Stannowski
Presenter / Speaker: D. Erfurt, HZB, Berlin, Germany
Event: Conference Conference
Session: 2BO.3 Dopant Free Heterojunctions and TCOs
Type(s) of Access:  Conference Registration
Topic: 2. 3 Low Temperature Route for Si Cells
Summary / Abstract: High-mobility transparent conductive oxides (TCOs) provide a high potential gain in short circuit current density (Jsc) in Silicon Heterojunction (SHJ) solar cells due to low parasitic absorption. For this reason high-mobility TCOs found their way already to industrial scale. However, for highly efficient SHJ solar cells the TCOs must fulfill several demands. Not only a high Jsc is required, but also a sufficiently low TCO sheet resistance and a low contact resistance to the n- and p-doped Si layers. Also the passivation of the SHJ solar cells must not be damaged during the TCO deposition (sputter damage) or a required subsequent annealing. We investigate industrially relevant, sputtered high-mobility TCOs of their ability to fulfill these requirements and their performance in bifacial rear-junction SHJ solar cells. Besides the commonly used tin-doped indium oxide (ITO), deposited at Helmholtz-Zentrum Berlin (HZB) or Von Ardenne GmbH, we will show studies of the high-mobility TCO SCOT and a newly developed material “XY”, which due to its novelty is not yet fully investigated. The opto-electrical properties of the TCOs on glass are compared and benchmarked. The lateral conductivity of the TCOs and the contact resistivity of TCO/Ag are obtained by the transfer length method (TLM). The contact resistivity of the TCOs and the n- and p-doped Si layers is modeled by Ag/TCO/nc-Si:H(n)/a-Si:H(i)/c-Si(n) and Ag/TCO/a-Si:H(p)/a-Si:H(i)/c-Si(p) symmetric samples, following the research of [1, 2]. Here, also the influence of the p-type Si-wafers’ conductivity is studied. The overall series resistance will be further analyzed due to the different contributions [3]. The hydrogenated Si layers are grown by plasma enhanced chemical vapor deposition (PECVD). To investigate the passivation properties of solar cell, equivalent samples are fabricated and the injection-dependent effective charge carrier lifetime (eff) is obtained by quasi steady-state photo conductance decay (QSSPC) measurements. We analyze the eff curves and the calculated implied open circuit voltage (i-Voc) and implied fill-factors (i-FF) before and after TCO deposition and after a thermal annealing, as required for screen print curing. The TCOs are tested on the front and rear side in different combinations. The results of the solar cells, the contact resistivity-test samples, passivating properties of the test samples and the opto-electrical properties are compared. In first experiments we indeed found that the high-mobility “SCOT” leads in median to an improved Jsc by up to 0.3 mA cm-2 compared to the reference sample when applied as the front-contact. Moreover, the samples show comparably low series resistances, high FF and Voc leading median efficiencies of 22.5 %, higher than the reference samples. Moreover, also when SCOT is applied as the back-contact the respective solar cells show higher Jsc and overall efficiencies. By the means of the conference further investigations to deepen the understanding will be carried out.