Optimization of Intrinsic ZnO Thickness in Cu(In,Ga)Se2-Based Thin Film Solar Cells

Abstract

The typical structure of high efficiency Cu(InGa)Se2 (CIGS)-based thin film solar cells is substrate/Mo/CIGS/CdS/i-ZnO/ZnO:Al(AZO) where the sun light comes through the transparent conducting oxide (i.e., i-ZnO/AZO) side. In this study, the thickness of an intrinsic zinc oxide (i-ZnO) layer was optimized by considering the surface roughness of CIGS light absorbers. The i-ZnO layers with different thicknesses from 30 to 170 nm were deposited via sputtering. The optical properties, microstructures, and morphologies of the i-ZnO thin films with different thicknesses were characterized, and their effects on the CIGS solar cell device properties were explored. Two types of CIGS absorbers prepared by three-stage co-evaporation and two-step sulfurization after the selenization (SAS) processes showed a difference in the preferred crystal orientation, morphology, and surface roughness. During the subsequent post-processing for the fabrication of the glass/Mo/CIGS/CdS/i-ZnO/AZO device, the change in the i-ZnO thickness influenced the performance of the CIGS devices. For the three-stage co-evaporated CIGS cell, the increase in the thickness of the i-ZnO layer from 30 to 90 nm improved the shunt resistance (RSH), open circuit voltage, and fill factor (FF), as well as the conversion efficiency (10.1% to 11.8%). A further increas of the i-ZnO thickness to 170 nm, deteriorated the device performance parameters, which suggests that 90 nm is close to the optimum thickness of i-ZnO. Conversely, the device with a two-step SAS processed CIGS absorber showed smaller values of the overall RSH (130–371 Ω cm2) than that of the device with a three-stage co-evaporated CIGS absorber (530–1127 Ω cm2) ranging from 30 nm to 170 nm of i-ZnO thickness. Therefore, the value of the shunt resistance was monotonically increased with the i-ZnO thickness ranging from 30 to 170 nm, which improved the FF and conversion efficiency (6.96% to 8.87%).

SnO2/ZnO Heterostructure as an Electron Transport Layer for Perovskite Solar Cells

“…The synthesis parameters of the ZnO films were chosen considering a high transmittance in the visible region and good electrical conductivity, so as to be suitable as a contact electrode in a solar cell. As ZnO is cheap and non-toxic, it has already been exploited in CIGS 23 solar cells. The choice of SnO 2 /ZnO is suggested by the low temperature needed for their synthesis and their properties being, in principle, compatible, especially regarding their refractive indices, as shown in Table 1.…”

RF/DC Magnetron Sputtering Deposition of Thin Layers for Solar Cell Fabrication

“…Complex structure of Cu(In,Ga)Se 2 based solar cell requires a variety of technologies for particular layer fabrication to achieve high device efficiency. This is the reason why co-evaporation method is the most used one in the process of CIGS absorber fabrication [10][11][12] while chemical bath deposition (CBD) is a very common method of CdS buffer layer fabrication [13,14]. The application of optimal methods for each structure fabrication leads to the highest efficiency of the final device.…”

“…Figure 12 shows X-ray diffraction pattern of highly resistive i-ZnO deposited on SLG substrate at 200 • C. Similarly to the previous studies on ZnO:Al [20], a large, intense peak located at 33.93 • which corresponds to the hexagonal polycrystalline structure with (002) plane was observed (according to the JCPDS Card No. 00-001-1136 [10]). The average grain size calculated from FWHM of (002) diffraction peak was about 10 nm.…”

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphologies

“…Once doped, they display new properties, e.g., electrical conductivity, magnetic, magneto-optical, photocatalytic, antibacterial and optical [ 74 , 161 , 220 , 221 , 222 , 223 , 224 , 225 , 226 , 227 , 228 , 229 , 230 , 231 , 232 ]. At present, various ZnO nanostructures are being used in attempts to produce a new generation of light-emitting diodes [ 233 , 234 ], lasers [ 235 ], field emission devices [ 236 , 237 ], memory carriers [ 238 , 239 ], solar cells [ 240 , 241 , 242 , 243 , 244 , 245 , 246 ], liquid crystals [ 247 ], polymer nanocomposites [ 248 , 249 , 250 , 251 ], food packaging materials [ 252 , 253 , 254 , 255 , 256 , 257 , 258 ], transparent ultraviolet light absorbers in unplasticised polymers [ 259 ], catalysts [ 260 ], photoluminescent NPs [ 261 ], photocatalysts ...…”