Themed collection Emerging inorganic materials in thin-film photovoltaics

The lecture focuses on emerging chalcogenide-based thin-film photovoltaics and provides both an overview of selected absorber candidates that are of recent interest, and a deeper dive into an exemplary Cu₂BaSn(S,Se)₄-related family.

A summary of progress in the design, discovery and optimisation of sustainable materials for solar energy conversion is presented.

The rates of excited-state decay through recombination processes determine the usefulness of a semiconductor for ambipolar devices. We find that recombination rates in chalcogenide perovskites are promising for continued progress towards solar cells.

Cu/B^II disorder is significantly reduced with Mn incorporation and the kesterite–stannite structural phase transition in Cu₂(Zn,Mn)SnSe₄.

Ge doping is employed to aid the recrystallisation of Cu₂ZnSnS₄ nanocrystals. Opto-electrical properties are presented to describe Ge incorporation with a focus on the electronic interface between the Ge:Cu₂ZnSn(S, Se), absorber and CdS buffer layer.

Results show a low temperature atomic layer deposited (Zn,Sn)O buffer layer with optimum band alignment improves the translation of qFLs into V_OC and consequently reduces the deficit between the qFLs and V_OC of a Cu(In,Ga)S₂ solar cell.

Photoluminescence is used to predict the open circuit voltage. However, band gap fluctuations and tail states broaden the PL emission and can lead to underestimation of the quasi Fermi level splitting. We discuss potential errors and how to avoid them.

Massive increase of data sharing and full utilization of digitization is proposed to help accelerate novel PV material development.

The capability of chalcopyrites to accept group-I deficiency without decomposing varies greatly even within a narrow family of isomorphic I–III–VI systems. Only one-third of them exhibit this property at the level seen in Cu(In,Ga)Se₂.

Hard X-ray photoelectron spectroscopy reveals the (Cd,Zn)S:Ga/CuSbS₂ thin-film solar cell interface to be heavily intermixed resulting in a ‘cliff’-like conduction band offset.

A rapid thermal annealing process assists the synthesis of the preferred [003]-oriented Se thin film with a large grain size for photovoltaic application.

A two-step post-deposition treatment approach enables organic residue control in TiO₂ and improves the efficiency of a Sb₂Se₃/TiO₂ thin film solar cell.

Thickness reduction of kesterite CZTS solar cells down to 250 nm is performed showing relatively small performance loss. The introduction of oxide passivation layers improves performance and a NaF treatment is used to make such back contact conductive.

Ag-doped GeSe has been successfully grown and compared to undoped GeSe with XRD, photoemissions, ICP-OES and CV. The undoped and Ag-doped GeSe were included in PV devices with the champion device structure and J–V curve shown.

Zinc phosphide (Zn₃P₂) is a promising material for photovoltaic applications. Here, we investigate the effect of stoichiometry variations and defects on the structural and optoelectronic properties of monocrystalline Zn₃P₂.

Metastable defect structures can activate novel pathways for electron–hole recombination in semiconductors – particularly for inorganic compounds with anharmonic/mixed bonding, multinary composition, low symmetry and/or highly-mobile defects.

Scanning X-ray microscopy is shown to be powerful for in situ and operando studies of nanostructured devices such as CZTS solar-cells: nanoscale performance is correlated with composition, and observed trends are understood with simulations.

Oxygen alters the properties of semiconducting nitrides, such as ZnGeN₂. We study the effect of oxygen incorporation computationally and compare the results to experimental values obtained in the system Zn_1+xGe_1−x(N_1−xO_x)₂.

The passivation of defects associated with the Se deficiency on a rear surface of superstrate SbSe₃ is acheived by post-deposition annealing treatment (PAT) under Se ambiance. The PAT greatly improves the device performance, mainly V_oc and FF.