Semitransparent Thin-film Solar Cells Research Articles

Numerical study of semi-transparent thin film heterojunction p-CuO/nZnO/AZO/ITO solar cells device model using SCAPS-1D

In the current time, transparent and semitransparent solar cells in photovoltaic industry have drawn important attention owing to their potential use as solar windows, and energy harvesting devices for building, vehicle integration and flexible electronics. In this work, a semitransparent thin film heterojunction solar cells device structure of p-CuO/nZnO/AZO/ITO was numerically modeled using SCAPS-1D software tools. The cell’s performance was investigated in terms of the different material layer properties, such as the thickness and carrier concentration or doping level. The simulation results of copper based semi-transparent thin film solar cell (TFSC) as the bottom cell model indicates that the highest efficiency was achieved at 8.9116 %, with the thickness and carrier concentration of n-ZnO material layer set at 20 nm, and 5.0 x 1018 cm-3 respectively, whereas the thickness of CuO absorber layer was fixed at 110 nm. Finally, the overall results show that CuO based absorber layer exhibits potential as photoactive material particularly for semitransparent thin film solar cells applications.

Semitransparent Sb2S3 thin film solar cells by ultrasonic spray pyrolysis for use in solar windows.

The integration of photovoltaic (PV) solar energy in zero-energy buildings requires durable and efficient solar windows composed of lightweight and semitransparent thin film solar cells. Inorganic materials with a high optical absorption coefficient, such as Sb2S3 (>105 cm−1 at 450 nm), offer semitransparency, appreciable efficiency, and long-term durability at low cost. Oxide-free throughout the Sb2S3 layer thickness, as confirmed by combined studies of energy dispersive X-ray spectroscopy and synchrotron soft X-ray emission spectroscopy, semitransparent Sb2S3 thin films can be rapidly grown in air by the area-scalable ultrasonic spray pyrolysis method. Integrated into a ITO/TiO2/Sb2S3/P3HT/Au solar cell, a power conversion efficiency (PCE) of 5.5% at air mass 1.5 global (AM1.5G) is achieved, which is a record among spray-deposited Sb2S3 solar cells. An average visible transparency (AVT) of 26% of the back-contact-less ITO/TiO2/Sb2S3 solar cell stack in the wavelength range of 380–740 nm is attained by tuning the Sb2S3 absorber thickness to 100 nm. In scale-up from mm2 to cm2 areas, the Sb2S3 hybrid solar cells show a decrease in efficiency of only 3.2% for an 88 mm2 Sb2S3 solar cell, which retains 70% relative efficiency after one year of non-encapsulated storage. A cell with a PCE of 3.9% at 1 sun shows a PCE of 7.4% at 0.1 sun, attesting to the applicability of these solar cells for light harvesting under cloud cover.

Effect of Ag-doping on the structural, optical, electrical and photovoltaic properties of thermally evaporated Cadmium Selenide thin films

To study the capability of the CdSe thin films to use as an absorber layer in semi-transparent thin film solar cells, the structural, optical, electrical and photovoltaic properties of thermally evaporated CdSe thin films (thickness 300 nm) as a function of silver-doping were investigated. A novel and facile method was used to Ag-doping of the samples. Some aqueous solution of silver nitrate (with various concentration) was spin coated onto the surface of CdSe thin films followed by air-annealing to diffuse silver dopants into the layers. The field emission scanning electron microscope (FE-SEM) images showed that the surface of CdSe thin films was improved with our doping method. X-ray diffraction (XRD) analysis revealed the hexagonal structure of the samples. The crystallite size, micro-strain and dislocation density of CdSe thin films were evaluated using XRD patterns. The transmittance spectra in the wavelength range of 400–2500 nm were measured and then used to study other optical parameters. The optical energy band gap was decreased with Ag-doping from 1.96 eV to 1.67 eV. The electrical conductivity of FTO/CdSe:Ag/Al Schottky junction devices was improved by Ag-doping, and the photovoltaic efficiency was increased by Ag-doping form 1.53% for the undoped sample to 2.78% for the sample with the highest doping concentration. Obtained results show that Ag-doped CdSe thin films are a promising candidate to use as an absorber layer in semi-transparent solar cells and colorful photovoltaic windows.

Adoption of wide-bandgap microcrystalline silicon oxide and dual buffers for semitransparent solar cells in building-integrated photovoltaic window system

We focused on developing penetration-type semitransparent thin-film solar cells (STSCs) using hydrogenated amorphous Si (a-Si:H) for a building-integrated photovoltaic (BIPV) window system. Instead of conventional p-type a-Si:H, p-type hydrogenated microcrystalline Si oxide (p-μc-SiOx:H) was introduced for a wide-bandgap and conductive window layer. For these purposes, we tuned the CO2/SiH4 flow ratio (R) during p-μc-SiOx:H deposition. The film crystallinity decreased from 50% to 13% as R increased from 0.2 to 1.2. At the optimized R of 0.6, the quantum efficiency was improved under short wavelengths by the suppression of p-type layer parasitic absorption. The series resistance was well controlled to avoid fill factor loss at R = 0.6. Furthermore, we introduced dual buffers comprising p-a-SiOx:H/i-a-Si:H at the p/i interface to alleviate interfacial energy-band mismatch. The a-Si:H STSCs with the suggested window and dual buffers showed improvements in transmittance and efficiency from 22.9% to 29.3% and from 4.62% to 6.41%, respectively, compared to the STSC using a pristine p-a-Si:H window.

Semi-transparent photovoltaics using ultra-thin Cu(In,Ga)Se2 absorber layers prepared by single-stage co-evaporation

Semi-transparent thin-film solar cells with ultra-thin Cu(In,Ga)Se2 (CIGS) absorber layers were fabricated on fluorine-doped tin oxide coated glass substrates using a single-stage co-evaporation process. The effects of the deposition conditions, such as the absorber thickness, deposition temperature, and post-deposition treatment using NaF on the material properties of the CIGS films were evaluated. In addition, the power conversion efficiency (PCE) and average visible transmission (AVT) in the wavelength range of 420–720 nm for semi-transparent CIGS solar cells using these absorber layers were systematically investigated. The AVT of the solar cells was directly dependent on the thickness of the CIGS absorber films. When the film thickness of the absorber layers increased from 300 nm to 950 nm, the AVT decreased gradually from 9.04% to 0.30%, while their PCE values did not show a clear dependence on the absorber thickness. Narrow columnar grains were observed in the microstructure of the ultra-thin CIGS absorber layers, irrespective of the film thickness and deposition temperature. Doping the ultra-thin CIGS absorber layers with Na after film deposition enhanced solar cell performance (the open circuit voltage (VOC) and fill factor (FF) were improved). The enhanced cell performance was attributed to the lack of a resistive GaOx film at the CIGS/FTO interface and thermal damage to the FTO back contact. The PCE values of semi-transparent solar cells with ultra-thin CIGS absorber layers prepared under the optimal deposition conditions varied from 6.46% to 9.78% when the CIGS absorber thickness was varied from 200 nm to 300 nm, respectively, while the corresponding AVT values changed from 18.59% to 9.04%.

Semi-transparent thin film solar cells by a solution process

Easily processed, low cost, and highly efficient solar cells are desirable for photovoltaic conversion of solar energy to electricity. We present the fabrication of precursor solution processed CuInGaS2 (CIGS) thin film solar cells on transparent indium tin oxide (ITO) substrates. The CIGS absorber film was prepared by a spin-coating method, followed by two successive heat treatment processes. The first annealing process was on a hot plate at 300 °C for 30 min in air to remove carbon impurities in the film; this was followed by a sulfurization process at 500 °C in an H2S(1%)/Ar environment to form a polycrystalline CIGS film. The absorber film with an optical band-gap of 1.52 eV and a thickness of about 1.1 µm was successfully synthesized. Because of the usage of a transparent glass substrate, a bifacial CIGS thin film device could be achieved; its power conversion efficiency was measured to be 6.64% and 0.96% for front and rear illumination, respectively, under standard irradiation conditions.