Post‐treatment of Cu(In,Ga)Se2 (CIGS) surfaces, as an efficient way to improve the performance of CIGS solar cells, has received increasing attention in recent years. To alleviate the limitations of the as‐grown CIGS thin films, such as oxidation, Na accumulation, and microstructure of CIGS surface, ammonia (NH3) etching solution was introduced to post‐treat the CIGS surface to improve its quality in this study. To investigate the mechanisms of NH3 etching effects on the CIGS surfaces and the resulted devices, a series of NH3 solution treatments, of different concentrations, on CIGS films is carried out and the resulted surfaces and devices are carefully examined. It is demonstrated that proper concentration of NH3 solution could not only result in a new microstructure between CIGS and Zn(O,S) thin films but also improve the performance of the Zn(O,S) based CIGS solar cells, especially in terms of the device fill factor. As a result, a Zn(O, S) based CIGS solar cell with a conversion efficiency of over 20% is obtained with application of NH3 treatment together with MgF2 anti‐reflective coating. Furthermore, it is found that NH3 treatment could effectively reduce the undesired light soaking effect, which often appears in the Zn(O,S) based CIGS solar cells.

Reducing Cu(In,Ga)Se 2 (CIGS) absorber thickness into submicron regime provides an opportunity for reducing CIGS solar cell manufacturing time and cost. However, CIGS with submicron-thick absorber would suffer strong absorption loss in the long-wavelength region. In this paper, we report a new fabrication route for CIGS solar cells on soda-lime glass substrates with different Ga content (0.

Two-dimensional graphene has tremendous potential to be used as a transparent conducting electrode (TCE), owing to its high transparency and conductivity. To date graphene films have been applied to several kinds of solar cells except the Cu(In, Ga)Se₂ (CIGS) solar cell. In this work, we present a novel TCE structure consisting of a doped graphene film and a thin layer of poly(methyl methacrylate) (PMMA) to replace the ZnO:Al (AZO) electrode for CIGS. By optimizing the contact between graphene and intrinsic ZnO (i-ZnO), a high power conversion efficiency (PCE) of 13.5% has been achieved, which is among the highest efficiencies of graphene-based solar cells ever reported and approaching those of AZO-based solar cells. Besides, the active area of our solar cells reaches 45 mm(2), much larger than other highly efficient graphene-based solar cells (>10%) reported so far. Moreover, compared with AZO-based CIGS solar cells, the total reflectance of the graphene-based CIGS solar cells is decreased and the quantum efficiency of the graphene-based CIGS is enhanced in the near infrared region (NIR), which strongly support graphene as a competitive candidate material for the TCE in the CIGS solar cell. Furthermore, the graphene/PMMA film can protect the solar cell from moisture, making the graphene-based solar cells much more stable than the AZO-based solar cells.