Optimisation of Metallic Interconnecting Layer in Homo-Tandem Cells
Blaise Godefroid a, Gregory Kozyreff a
a Université libre de Bruxelles, av. F. D. Roosevelt 50, Bruxelles, 1050, Belgium
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Blaise Godefroid, 085
Publication date: 11th February 2019

In this communication, we emphasize the effect of inserting an ultra-thin metal film (UTMF) in the interconnecting layers (ICL) of series-connected (2T for two-terminal) homo-tandems. The cell geometry is optically designed to maximize absorption of the AM1.5 spectrum. We numerically demonstrate large improvements in cell performance thanks to the insertion of an UTMF. For example, with DBP:C70, a gain from 6.3 mA/cm² to 7.5 mA/cm² is computed. The optimal thickness of the UTMF is found to be relatively thick (~10 nm). These observations, together with the other ones reported here, are valid for a wide choice of organic materials: PTB7-th:PC71BM, P3HT:PC61BM and DBP:C70 as well as a theoretical material with an absorption spectrum given by a step function plus an Urbach tail. This last idealized response is found to reliably model real materials.

Our results are compared to those obtained with a parallel (3T) homo-tandem cell and with a single cell [1]. Thus, for each active material, we examine four configurations (referred to as A, B, C, and D in the TOC Graphic).

We find that a major design parameter is the maximum allowed thickness, Lmax, of the active material. Knowing this parameter, we can determine which of the four configurations achieves the best performances. In general, B gives the best result. However, from a manufacturing point of view, this configuration has the disadvantage of requiring an electrical contact to the central UTMF, contrary to its series counterpart D. This last one is then a good candidate to improve performance without too complicated manufacturing. Indeed, D achieves better performances than A and C for Lmax < 200 nm and even comparable to B for Lmax < 100 nm.

The above analysis is carried out with two front electrodes: ITO and a recently devised ITO-free alternative, the Two-Resonance Tapping Cavity (TRTC) [2]. We show that for very thin active materials (Lmax < 90 nm), the TRTC electrode gives similar results to ITO for B and D and is better for C. For larger materials, ITO is better except for A and for Lmax < 150-200 nm. Hence, the TRTC front electrode seems to be a good alternative to ITO, particularly for thin active materials.

We thank Jordi Martorell (ICFO, The Institute of Photonic Sciences) for helpful discussions and for communicating their data.

© Fundació Scito
We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info