TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Device: The diffuser comprises dielectric particles. The dielectric particles are covered with white paint, where the white paint comprises titanium oxide (TiO2). The dielectric particles have diameters of about 0.2-2.0 mu m. The diffuser comprises metal particles, where the metal particles have diameters of about 150-200 nm. The PV device further comprises a dielectric layer disposed below the metal particles, where the dielectric layer comprises silicon oxide (SiO2), silicon nitride (SiN), or glass. The PV device further comprises a reflective layer disposed below the diffuser. The window layer comprises AlGaAs. The antireflective coating comprises magnesium fluoride (MgF2), zinc sulfide (ZnS), SiN, titanium oxide (TiO2), SiO2, or their combination. A surface of the window layer adjacent to the antireflective coating has been roughened to provide different angles for increased light trapping. The PV device further comprises particles interposed between the window layer and the antireflective coating to provide different angles for increased light trapping, where the particles comprise polystyrene spheres. The window layer comprises a first window layer disposed above the n-doped layer; and a second window layer disposed above the first window layer. The first window layer and the second window layer comprise AlGaAs, but with different compositions. The first window layer is doped and the second window layer is undoped. A surface of the second window layer adjacent to the antireflective coating has been roughened to provide different angles for increased light trapping. The PV device further comprises particles interposed between the second window layer and the antireflective coating to provide different angles for increased light trapping. A bottom surface of the p+-doped layer has been roughened to provide different angles for increased light trapping. The PV device further comprises particles disposed below the p+-doped layer to provide different angles for increased light trapping, where the particles comprise polystyrene spheres. The PV device further comprises contacts for external connection coupled to the n-doped and the p+-doped layers, such that the contacts for external connection are disposed below the p-n layer and do not block the light from reaching the p-n layer through the antireflective coating and the window layer. The contacts comprise n-contacts coupled to the n-doped layer; and p-contacts coupled to the p+-doped layer. The n-contacts are disposed within recesses in the p+-doped layer and the p-contacts are disposed below the p+-doped layer, where lateral surfaces of the recesses in the p+-doped layer are passivated. The PV device further comprises an interface layer interposed between the p+-doped layer and the p-contacts, where the interface layer comprises pt-GaAs. The contacts comprise PdGe. The PV device further comprises an intermediate layer interposed between the n-doped layer and the p+-doped layer. The p-n layer formed between the n-doped layer and the p+-doped layer is an offset p-n layer. The p+-doped layer has a doping profile fine-tuned such that doping levels increase from one side of the p+-doped layer to the other. The n-doped layer or the p+-doped layer comprises a monocrystalline group III-V semiconductor. The n-doped layer comprises n-GaAs. The p+-doped layer comprises p+-AlGaAs.