Muonium as isolated hydrogen in solar cell material Cu(In,Ga)Se2

Cu(In,Ga)Se2 is a potential absorber material for solar cell applications. Hydrogen (H) impurities in semiconductors are ubiquitous and unavoidable due to its abundance and reactivity. Trace amounts of isolated H can significantly affect the electrical, optical, magnetic, and structural properties of a host. It is therefore imperative, for efficient and effective device development, to understand the role and effect isolated H impurities have in materials relevant for applications. One of the only ways to study isolated H is Muon Spin Rotation/Relaxation/Resonance (MuSR) which utilizes 100% spin polarized, positive muons (S=1/2, 1/9 m_{P+}) that, when implanted in a host, function as an experimentally accessible analogue to isolated H (i.e. light isotope of H). We have completed TF-, LF-, and ZF-MuSR measurements on Cu(In,Ga)Se2 to characterize Mu (isolated H impurity). Ultimately, we find there are two stopping sites for the implanted Mu (H) and with increased thermal energy a transition from a static state to trap-limited diffusion, and on to global diffusion (E_{A} = 284 +/- 35 meV). Here, we present an overview of the MuSR technique and results from measurements on Cu(In,Ga)Se2.