TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Stack: In the photovoltaic stack, the AL is between and contacts the top electrode and the bottom electrode. The top electrode is selected from gold (Au), silver (Ag), platinum (Pt), palladium (Pd), nickel (Ni), molybdenum trioxide (MoO3), and its combinations. The SNPs are selected from PbS, lead selenide (PbSe), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), lead telluride (PbTe), zinc sulfide (ZnS), zinc telluride (ZnTe), zinc selenide (ZnSe), and core-shell nanoparticles. The SNPs comprise PbS colloidal quantum dots having a diameter from about 2 nm to about 10 nm. SNPs comprise PbS colloidal quantum dots having about the same sizes. The photovoltaic stack further comprises halide ions bonded to the quantum dot's surface; and where the halide ions are selected from fluoride, bromide, chloride, iodide, and its combinations. The PNP comprises a spherical dielectric core having an average diameter of about 25 nm to about 100 nm; a metal shell surrounding the core and having an average thickness of about 2 nm to 50 nm; and, optionally an insulating shell surrounding the metal shell having an average thickness of about 2 nm to 50 nm. The dielectric core is selected from silicon dioxide (SiO2), silicon nitride (Si3N4), polystyrene, insulating polymers, and insulating metal oxides. The metal is selected from copper (Cu), silver (Ag), Au, Pt, Pd, Ni, aluminum (Al), and its combinations. The core is SiO2, the metal shell is Au, and the insulating shell is polyvinylpyrrolidone (PVP); or the core is SiO2 and has a diameter of about 60 nm; and where the metal shell is Au and has a thickness of about 15 nm. Preferably, the core has an average diameter of about 120 nm and the metal shell has an average thickness of about 15 nm. The core has an average diameter of about 50 nm and the metal shell has an average thickness of about 15 nm. The PNP has an average diameter of about 50 nm to about 80 nm. It has an average diameter of about 65 nm or about 75 nm. The PNP is selected from PNP above, nanorods having an average diameter of about 50 nm to about 70 nm and an average length of about 450 nm to about 550 nm, and nanospheres having an average diameter of about 100 nm to about 200 nm. The PNP is a nanorod or a nanosphere and comprises a metal selected from Cu, Ag, Au, Pt, and its combinations. It has an average diameter of about 150 nm or less. At least one PNP is positioned about 50% to about 85% of the thickness of the stack from the top electrode; at least one PNP is positioned about 60% to about 70% of the thickness of the stack from the top electrode; at least one PNP is positioned about 65% of the thickness of the stack from the top electrode; or at least one PNP is positioned about 66.6% of the thickness of the stack from the top electrode. At least one PNP is positioned about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, or 390 nm from the top electrode; at least one PNP is positioned about 100, 150, 200, 250, 300, or 350 nm from the top electrode; at least one PNP is positioned about 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 nm from the top electrode; or at least one PNP is positioned about 260 nm from the top electrode. The stack has a thickness of about 400 nm. It has a thickness of about 375 nm to about 425 nm. The bottom electrode is selected from FTO, ITO, TiO2/FTO, ZnO/TiO2/FTO, TiO2/ITO, ZnO/TiO2/ITO, and aluminum-doped ZnO (AZO)/FTO. It comprises a depleted heterojunction (DHL) that contacts the AL. The bottom electrode is transparent to visible light. The top electrode is the illuminated surface when the photovoltaic is used to generate a photocurrent. The thickness of the top electrode is about 0.1 nm to about 100 nm. The thickness of the photovoltaic stack is about 300 nm to about 400 nm; or the thickness of the photovoltaic stack is about 400 nm. Thickness of the AL is about 50 nm to about 500 nm; or thickness of the AL is about 300 nm to about 400 nm. The thickness of DHL is about 5 nm to about 200 nm. The photovoltaic stack comprises about 2 to about 15 PNPs per mu m. It has about 10 PNPs per mu m2. The PNP has a scattering-to- absorption ratio, S=scattering/absorption, that is greater than 1 for wavelengths ranging from 400 nm to 1200 nm, preferably S is substantially greater than 1, S is greater than 1.5, S is greater than 2, S is greater than 3. The PNP has a localized surface plasmon resonance (LSPR) centered around a wavelength of 600, 650, 700, 750, 800, 850, 900, 950, or 1000 nm. It has a LSPR centered around 800 nm or around 820 nm. It has a LSPR with a full width at half maximum (FWHM) of 100, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340 or 350 nm. The FWHM is 280 nm. The SNP has a bandgap excitation wavelength in the range 700 nm to 1.6 mu m. Preferred Composition: In the composition, the SNPs are selected from infrared absorbing PbS colloidal quantum dots. The SNPs comprise PbS colloidal quantum dots having about the same or different sizes. The composition further comprises halide ions bonded to the quantum dot's surface; and where the halide ions are selected from fluoride, bromide, chloride, iodide, and its combinations. The PNP comprises a spherical dielectric core having an average diameter of about 25 nm to about 100 nm; a metal shell surrounding the core and having an average thickness of about 2 nm to 50 nm; and, optionally an insulating shell surrounding the metal shell. At least one PNP is positioned about 15% to about 50% of the thickness of the composition from the electrode; at least one PNP is positioned about 30% to about 40% of the thickness of the composition from the electrode; at least one PNP is positioned about 35% of the thickness of the composition from the electrode; or at least one PNP is positioned about 33.3% of the thickness of the composition from the electrode. The thickness of the composition is about 100, 200, 300, 400 (preferred), or 500 nm. The electrode is selected from FTO, ITO, TiO2/FTO, ZnO/TiO2/FTO, TiO2/ITO, and ZnO/TiO2/ITO. It comprises a depleted heterojunction that contacts the AL. The SNP has a bandgap excitation wavelength of about 980 nm. Preferred Medium: In the medium, the PNP/SNP number-of-particles ratio is about 1:5; 1:10; 1:15; 1:20; 1:25; 1:50: 1:100; 1:250; 1:500; 1:1000; or 1:10000. The PNP/SNP number-of-particles ratio is about 1:10,000; 1:100,000; 1:1000000; or 1:10000000. Preferred Method: In preparing the photovoltaic, the first AL is twice the thickness of the second AL.