Perovskite/Silicon tandem solar cells: elaboration of the transparent P-type interfacial layer and transparent front electrode
Rafik Benrabbah a, Delfina Munoz a, Matthieu Manceau a, Solenn Berson a, Florence Ardiaca a
a CEA, LITEN, Department of Solar Technologies, INES, 50 avenue du Lac Leman BP 332, Le Bourget du Lac, 73377, France
Proceedings of Perovskite Thin Film Photovoltaics (ABXPV17)
València, Spain, 2017 March 1st - 2nd
Organizers: Henk Bolink and David Cahen
Oral, Solenn Berson, presentation 048
Publication date: 18th December 2016

In the context of the increase of the photovoltaic (PV) technologies, the question of the cost remains central. Indeed, the price of the electricity reached by this technology remains high with regard to the conventional energies.

The current strategy to remain competitive articulates around two main strategies: the increase of the efficiency of the PV cells and the decrease of the costs linked to the raw material. In this context, our teams work to combine on one hand heterojunction amorphous / crystalline silicon cells (HJT) and on the other hand perovskite (CH3NH3PbI3) ones to obtain a 2-terminal tandem device in standard architecture with the target of highly efficient conversion up to 30 %. 

The first stage of the project concerned the perovskite sub-cell development for which we concentrated on two axes of studies: i) the elaboration of a transparent hole extraction layer (P-type) at the front side of the cell as well as ii) the elaboration of a Transparent Conductive Oxyde (TCO) front electrode.

Concerning the P type interfacial layer, we suggested studying 3 main classes of materials: a conductive oxide (WO3), an organic molecular semiconductor (Spiro-MeOTAD) and a conductive polymer (PEDOT:PSS). These 3 materials show a high transparency in the wavelength range of the absorption of the active perovskite layer and can be processed in solution. After being characterized in PV device, the PEDOT: PSS containing cell gave the best performances in terms of conversion efficiency. The performances were comparable to those obtained in the standard conditions for single junction opaque cell.

About the TCO, Indium Tin Oxyde (ITO) layers were processed by PVD (Physical Vapor Deposition). We had to adapt the process for a deposition at room temperature taking into account the risk of degradation of the high-temperature sensitive perovskite material if processed above 150°C. Thus we optimized the parameters to improve the transparency/resistivity of the layer by varying the power of the plasma as well as the flows of argon and oxygen. Finally it was possible to obtain highly transparent (>80%) and low resistive ( ITO in optimized conditions without degradation of the properties of the perovskite layer nor the performances of PV cells as prepared. 

The next step is now to integrate the perovskite sub-cell onto HJT to elaborate tandem device to reach high performances.

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