Data-Driven Tunnel Oxide Passivated Contact Solar Cell Performance Analysis Using Machine Learning.

Tunnel oxide passivated contacts (TOPCon) have gained interest as a way to increase the energy conversion efficiency of silicon solar cells, and the International Technology Roadmap of Photovoltaics forecasts TOPCon to become an important technology despite a few remaining challenges. To review the recent development of TOPCon cells, this work has compiled a dataset of all device data found in current literature, which sums up to 405 devices from 131 papers. This may seem like a surprisingly small number of cells given the recent interest in the TOPCon architecture, but it illustrates a problem of data dissemination in the field. Notwithstanding the limited number of cells, there is a great diversity in cell manufacturing procedures, and this work observes a gradual increase in performance indicating that the field has not yet converged on a set of best practices. By analyzing the data using statistical methods and machine learning (ML) algorithms, this work is able to reinforces some commonly held hypotheses related to the performance differences between different device architectures. This work also identifies a few more unintuitive feature combinations that would be of interest for further experimentally studies. This work also aims to inspire improvements in data management and dissemination within the TOPCon community.

Aluminum and Molybdenum Co-Doped Zinc Oxide Films as Dual-Functional Carrier-Selective Contact for Silicon Solar Cells.

Aluminum-doped zinc oxide (AZO) is considered as a promising candidate as transparent conductive oxide (TCO) for silicon heterojunction solar cells due to its high carrier density, nontoxic nature, and low cost. Herein, it is presented that the transparency of the AZO film can be optimized through co-sputtering of AZO and molybdenum oxide (MoOx). Furthermore, aluminum and molybdenum co-doped zinc oxide (MAZO) can be used as both the TCO layer and electron-selective contact (ESC) for silicon heterojunction solar cells. The surface morphology, cation oxidation state, and optical and electrical properties of all MAZO films are characterized. It is found that the transmittance of all MAZO films is significantly increased at a wavelength of 450-800 nm due to MAZO with a stronger Zn-O bond and a wider band gap. The conductivity of MAZO films is approximate to AZO films at a low MoOx target deposit power (50 W), and the sheet resistance of MAZO films increases significantly by increasing the deposition power up to 100 W. Finally, the optimized MAZO films are used as TCO and ESC for silicon heterojunction solar cells, showing a power conversion efficiency of 19.58%. The results show an effective stage to improve the optical properties of AZO through co-doping and the possibility of applying MAZO as a dual-functional layer for silicon solar cells.

Broad-Spectrum Ultrathin-Metal-Based Oxide/Metal/Oxide Transparent Conductive Films for Optoelectronic Devices.

High-quality transparent conductive materials are beneficial to improve the charge transfer and light transmittance and reduce the interface defects as well as the production cost of optoelectronic devices. A high threshold thickness of metal layer in oxide/metal/oxide (OMO) compound thin films leads to strong reflectance, especially in the near-infrared region, limiting the broad-spectrum device applications. Here, we propose a novel Zn doping strategy using the low-cost single-target sputtering technology to achieve the growth of Ag-Zn thin films (i.e., Zn-doped Ag) and introduce a trace amount of O2 to further obtain ultrathin Ag-Zn(O) films (thin-film thickness d ≤ 5 nm), which greatly improves the broad-spectrum characteristics of OMO films. Heterogeneous metal and gas doping technology effectively promotes the formation of two-dimensional continuous film growth. By combining the ultrathin Ag-Zn(O) layer with the MGZO (i.e., Mg- and Ga co-doped ZnO) oxide film grown by reactive plasma deposition, a typical broad-spectrum MGZO/Ag-Zn(O)/MGZO (50/5/50 nm)-OMO compound thin film exhibits an average transmittance of 91.6% in the wavelength range of 400-1200 nm and low sheet resistance. The broad-spectrum organic solar cells based on MGZO/Ag-Zn(O)/MGZO electrodes present a high power conversion efficiency of 15.35%, superior to those devices based on single-layer oxide electrodes. The distinguished performances are attributed to the ultrathin Ag-Zn(O) films in OMO, paving the way for applications in broad-spectrum optoelectronic and flexible electronic devices.

Manipulated Crystallization and Passivated Defects for Efficient Perovskite Solar Cells via Addition of Ammonium Iodide.

Organic-inorganic metal halide perovskite materials have been widely studied as the light absorber for efficient photovoltaics. However, perovskite layers with defective nature are typically prepared with an uncontrollable crystallization process, intrinsically limiting further advance in device performance, and thus require delicate manipulation of crystallization processes and defect density. Here, we demonstrate an ammonium-assisted crystallization of perovskite absorbers during a two-step deposition to fabricate efficient solar cells. Addition of ammonium iodide (NH4I) is devised to manipulate the nucleation and crystal growth of perovskite, wherein the formation and transition of intermediate x[NH4+]•[PbI3]x- enables high-quality perovskite layers with an enlarged grain and reduced defect density. As a result, the perovskite solar cells (PSCs) achieve an average efficiency of 21.36% with a champion efficiency of 22.15% and improved environmental stability over 30 days in ambient conditions with varied relative humidity. These results with addition of NH4I provide an available and ingenious way to construct high-quality perovskite layers for efficient solar cells and will advance the commercial application of perovskite-based photovoltaics.

Quasi-Heteroface Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted unprecedented attention due to their rapidly rising photoelectric conversion efficiency (PCE). In order to further improve the PCE of PSCs, new possible optimization path needs to be found. Here, quasi-heteroface PSCs (QHF-PSCs) is designed by a double-layer perovskite film. Such brand new PSCs have good carrier separation capabilities, effectively suppress the nonradiative recombination of the PSCs, and thus greatly improve the open-circuit voltage and PCE. The root cause of the performance improvement is the benefit from the additional built-in electric field, which is confirmed by measuring the external quantum efficiency under applied electric field and Kelvin probe force microscope. Meanwhile, an intermediate band gap perovskite layer can be obtained simply by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. Tunability of the band gap is obtained by varying the film thicknesses of the narrow and wide band gap layers. This phenomenon is quite different from traditional inorganic solar cells, whose band gap is determined only by the narrowest band gap layer. It is believed that these QHF-PSCs will be an effective strategy to further enhance PCE in PSCs and provide basis to further understand and develop the perovskite materials platform.

Application of metal nanowire networks on hydrogenated amorphous silicon thin film solar cells.

We demonstrate the application of metal nanowire (NW) networks as a transparent electrode on hydrogenated amorphous Si (a-Si:H) solar cells. We first systematically investigate the optical performances of the metal NW networks on a-Si:H solar cells in different electrode configurations through numerical simulations to fully understand the mechanisms to guide the experiments. The theoretically optimized configuration is discovered to be metal NWs sandwiched between a 40 nm indium tin oxide (ITO) layer and a 20 nm ITO layer. The overall performances of the solar cells integrated with the metal NW networks are experimentally studied. It has been found the experimentally best performing NW integrated solar cell deviates from the theoretically predicated design due to the performance degradation induced by the fabrication complicity. A 6.7% efficiency enhancement was achieved for the solar cell with metal NW network integrated on top of a 60 nm thick ITO layer compared to the cell with only the ITO layer due to enhanced electrical conductivity by the metal NW network.