Insights on the limiting factors of Cu2ZnGeSe4 based solar cells

Germanium-based wide band gap kesterite semiconductor Cu2ZnGe(S,Se)4 (CZGeSSe) is considered a very promising absorber compound as top cell in tandem devices. Autonomy to tailor the from ~1.47 eV (Cu2ZnGeSe4-CZGeSe) ~2.2 (Cu2ZnGeS4-CZGeS), well non-toxic constituents makes this strong candidate for further scientific exploration. However, record efficiency of Cu2ZnGeSe4 solar cells still significantly lower than those its predecessors Cu2ZnSn(SxSe1-x)4 (CZTSSe), Cu(In,Ga)Se2 (CIGS) and CdTe thin-film cells. The comprehensive understanding factors limiting performance based purpose work, by combining complete characterization morphological, structural, compositional optoelectronic properties absorbers Besides, an in-depth investigation main limitations carried out, specifically focusing on studying origin large VOC deficit, recombination mechanisms, electric transport properties, tails possible Cu2ZnGeSe4/CdS offset effects. champion CZGeSe device reported work shows 6.5%, Voc 606 mV, JSC 17.8 mA/cm2 FF 60%. results presented here demonstrate that voltage deficit could be mainly ascribed Fermi level pinning at interface, while modifications buffer layer induce “spike” p-n junction beneficial. Additionally, low carrier diffusion lengths lifetimes, along with back contact recombination, are identified culprits limited collection low-energy photons. Finally, some strategies proposed face overcome most these issues help improving performance.