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The behavior of carriers for an electron‐beam‐induced current (EBIC) evaluation is experimentally and theoretically analyzed for the polycrystalline Cu (In, Ga)Se2 (CIGS) thin‐film solar cells. The experimental EBIC signal in‐depth profiles of the CIGS layers show four features: peaks at grain boundaries (GBs), narrowed peaks near the surface, shifted peaks near the surface, and double peaks at the GBs and surface. Operating principles for CIGS solar cell devices under electron–hole pair excitation are systematically revealed utilizing a two‐dimensional theoretical EBIC simulation: (i) The EBIC peaks at the GBs are caused by a high hole barrier, including a valence band offset (ΔEV) and a band bending at the GBs; (ii) narrowing of EBIC peaks near the surface is caused by high defect densities at the GBs, grading of a conduction band minimum, and grading of acceptor concentration (Na) along with the CIGS depth direction; (iii) a shift in EBIC peaks near the surface is caused by high donor‐like defect densities at the surface; (iv) double peaks at the GBs and surface are caused by a thick surface layer (SL) with the ΔEV and the hole barrier at GBs. These findings of the EBIC analysis will help to comprehensively understand the complex polycrystalline CIGS carrier transport mechanism in realizing the highest‐efficiency CIGS solar cells. [ABSTRACT FROM AUTHOR]

In Cu(In,Ga)Se2 (CIGS) thin‐film solar cells, laterally inhomogeneous distributions of point defects may induce electrostatic potential fluctuations and thus reduce the open‐circuit voltage (Voc). In the present work, we investigate possible origins of fluctuating potentials and estimate the amplitude of fluctuations and Voc losses in solar cells with various [Ga] in the CIGS absorber, with different buffer layers and with different durations of an RbF postdeposition treatment (PDT). Electron‐beam‐induced current measurements were employed to study the local difference in the width of the space‐charge region (wSCR). It is shown that the amplitude of fluctuations in the wSCR depends significantly on the choice of buffer system and on the duration of the RbF PDT. In addition, energy‐dispersive X‐ray spectroscopy and cathodoluminescence measurements reveal that band‐gap fluctuations do not have substantial impact on the device performance. Finally, some of the investigated cells were exposed to light soaking, which was found to be a means to reduce the detected electrostatic potential fluctuations and also to increase the effective electron diffusion length in the CIGS absorber for a part of the investigated cells. [ABSTRACT FROM AUTHOR]