Alternative partner layer for thin film solar cells Nicole Fleck 1 , Devendra Tiwari 1 , Jon Major 2 , Frank Jaeckel 2 1 Northumbria University, United Kingdom, 2 University of Liverpool, Liverpool, UK
Cadmium Sulfide (CdS) is the most commonly employed partner layer in thin film solar cell technology. Despite the non-ideal band gap of 2.4 eV resulting in parasitic absorption and containing toxic cadmium, this layer has yet to be replaced by a suitable alternative. In this study, molybdenum-doped indium oxide (Mo:In 2 O 3 or IMO) is studied as a promising alternative partner layer for Sb 2 Se 3 solar cells. An additional challenge of Cd diffusion has been identified for this system. IMO has a suitably large bandgap and the stability of oxides which, in principle, could prevent interfacial interdiffusion. IMO also shows high carrier mobility and tunability of conduction band offset with Mo doping concentration [1], and thus has been proposed as a sustainable replacement to popular transparent conducting oxide – SnO 2 :In (ITO). Here we study the effect on device metrics as a function of IMO deposition temperature as well as device post-deposition annealing under inert (N 2 ) and air atmosphere conditions. The properties of sputtered IMO are found to depend strongly on the history of the sputtering target, which affects the morphology and structure of IMO layer, and in turn, the interface chemistry significantly. The spectral response of external quantum measurements indicates a presence of considerable recombination losses at Sb 2 Se 3 /IMO interface. To better understand the origin of the interfacial defects, compositional depth profiles are probed using secondary ion mass spectrometry, which points to extensive elemental-intermixing at the junction. Sb 2 Se 3 solar cell performances are also known to be sensitive to the presence of lattice mismatch with respect to base layer and oxygen content, which could also affect the observed device characteristics and is needed to be investigated further. This is the first demonstration of the use of IMO as a much-needed alternative buffer layer for Sb 2 Se 3 devices. The as-reported optimisation of deposition parameters for IMO films also open-up possibilities of its implementation in other emerging photovoltaic devices. References 1. Mater Horiz (2020)7:236
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