The chemical and electronic structures in the near-surface region of Cu(In,Ga)Se2 thin-film solar cell absorbers are investigated using nondestructive soft and hard X-ray photoelectron spectroscopy. In addition to a pronounced surface Cu-depletion, the [Ga]/([In]+[Ga]) composition indicates that the topmost surface is Ga-poor (or In-rich). For the studied depth region, common depth profiling techniques generally fail to provide reliable information and, thus, the near-surface chemical and electronic structure profiles are often overlooked. The relation between the observed near-surface elemental compositions and the derived electronic properties of the absorber material is discussed. It is found that the surface band gap energy crucially depends on the Cu-deficiency of the absorber surface and suggests that it is, in this region, only secondarily determined by the [Ga]/([In]+[Ga]) ratio.

Simultaneously enhancing device performance and longevity, as well as balancing the requirements on cost, scalability, and simplification of processing, is the goal of interface engineering of organic solar cells (OSCs). In our work, we strategically introduce antimony (Sb3+) cations into an efficient and generic n-type SnO2 nanoparticles (NPs) host during the scalable flame spray pyrolysis synthesis. Accordingly, a significant switch of conduction property from an n-type character to a p-type character is observed, with a corresponding shift in the work function (WF) from 4.01 ± 0.02 eV for pristine SnO2 NPs to 5.28 ± 0.02 eV for SnO2 NPs with 20 mol. % Sb content (ATO). Both pristine SnO2 and ATO NPs with fine-tuned optoelectronic properties exhibit remarkable charge carrier extraction properties, excellent UV resistance and photo-stability being compatible with various state-of-the-art OSCs systems. The reliable and scalable pristine SnO2 and ATO NPs processed by doctor-blading in air demand no complex post-treatment. Our work offers a simple but unique approach to accelerate the development of advanced interfacial materials, which could circumvent the major existing interfacial problems in solution-processed OSCs.