• Energy Research

An empirical method for estimating relative power losses caused by potential-induced degradation (PID) for p-type solar cells and modules using quantitative electroluminescence (EL) analysis (QELA) is presented. First, EL images are corrected for camera- and perspective distortion. The relative power loss map is then calculated from the logarithmic ratio of two EL images, taken either before and after PID degradation or at different applied currents. Only the cell average of the resulting power loss map is evaluated. The highest power loss across each string is averaged to obtain the overall power loss. Consequently, for modules with three strings, three cells are averaged. The resulting power loss depends on the current applied. The conversion to equivalent irradiance allows for comparison of measured and estimated device performance. The analysis of roughly 2000 EL images and related current–voltage ( I–V ) curves indicates a good agreement between flash-test-measured and performance estimated using QELA. A relative root mean square error of 1–3% can be achieved.

Efficiency and manufacturing cost are two key elements for the photovoltaic (PV) industry. In this paper, we look at the time-dependent evolution of efficiency and manufacturing cost for PV devices. For efficiency improvements, the empirical model developed by Goetzberger et al. is applied to describe the time-dependent improvements for a concrete technology in laboratory cell's research and development, and the learning factor c is extracted. The application of the Goetzberger's model is extended to industrial PV modules. It is forecasted that cadmium telluride (CdTe) and copper gallium indium diselenide (CIGS) will have the average module efficiency in 2020 of 17.9% and 16.4%, respectively. Over 21.8% commercial module efficiency is projected with n-type Si interdigitated back contact technology, while average module efficiencies of 17.4%, 18.4%, and 19.4% are projected for conventional p-type multi-, mono-, and mono-passivated emitter and rear cell (PERC), respectively. For the manufacturing cost, we parameterized the learning curve model of manufacturing cost for industrial crystalline silicon (c-Si), CdTe, and CIGS technologies. As projected by the learning curve, the manufacturing cost of c-Si and thin-film modules may reach 0.2 $/Wp or below, when the cumulative production reach 1 TW. The learning rate for Si (24.2%) is greater than CdTe (19.1%) and CIGS (8.1%).

AbstractThis work presents the comparison of measurement results for four types of encapsulated high‐efficiency c‐Si solar cells measured by 10 laboratories based in Asia, Europe and North America utilizing a wide range of voltage sweeping methods, which include well‐established procedures that represent good industry practice, as well as recently introduced ones that have not been verified yet. The aim of the round‐robin interlaboratory comparison was to examine the measurement comparability of different laboratories with respect to their measurement methods of high‐efficiency solar cells. A proficiency test was employed to examine the consistency of results and their corresponding uncertainties. The short‐circuit current (ISC) under STC measured by four accredited laboratories was firstly compared. In order to investigate the consistency related to the high device capacitance, the value of the ISC was fixed for all 10 participants. The results of all participant laboratories—compared via En number analysis—generally remained well within [−1; 1], thus indicating consistency between the measured values and the reference values within stated measurement uncertainties. The differences remained within ±1.15% in PMAX and within ±0.35% in VOC for all participants and methods applied. Correlations were observed among the PMAX, VOC, and FF differences from their weighted mean. An analysis of the effects of transient current (dQ/dt) at maximum power point caused by hysteresis effect on the measurement error of PMAX showed a significant linear correlation between error of maximum power and junction voltage sweep rate for heterojunction (HJT) solar cells. This work forms the basis to validate all applied methods and their stated measurement uncertainties.

AbstractThis paper reports on the latest advances in crystalline Si cells and modules in the industry and explores the dynamics shaping the silicon PV industry. First, we report on the recent efficiency improvements of passivated emitter and rear cell (PERC) and tunnel oxide passivated contact (TOPCon) cells on 210 mm wafers. At Trina Solar, the best batch average cell efficiency (total area) reached 23.61% for PERC and 25.04% for industrial‐TOPCon (i‐TOPCon). As far as we know, these are the highest values achieved on 210 mm wafers. The best champion efficiency for PERC and i‐TOPCon is 24.5% and 25.42%, respectively, as independently confirmed by the National Institute of Metrology of China in Beijing and ISFH CalTech in Hamelin. We have developed modules with power outputs of up to 660 W by using 66 pieces of these 210 mm cells with 12‐busbar technology in mass production. Besides, the aperture efficiency of the best laboratory PERC module fabricated by Trina Solar is 23.03%, which was independently confirmed by TÜV Rheinland. As far as we know, this is the first commercially sized PERC module with an aperture efficiency of 23% and a power output of over 600 W. Second, we have examined the technological development in the PV industry and summarise some empirical results. A look at the historical data shows that an increase in wafer area of at least 50% is required for a wafer size to become a new industry standard that lasts for 10 years. We find that it typically took about 3 years for the average efficiency of a cell in mass production to reach the efficiency of the champion cell produced in the industrial laboratory. We apply the empirical Goetzberger equation to analyse the module efficiency of c‐Si and thin‐film technologies. Based on our previous work, we update the selling price and manufacturing cost of PV modules and their learning curves. If we restrict the module price learning curve to the years starting in 2015, we find a short‐term learning rate (LR) of about 40%, while the overall LR since 1970 is about 24%. A strong LR is driven by collaboration among industrial players and clustering of the industry, as well as standardisation of the technology, the supply chain, and final product design, which lead to fast equipment development and fast increase in capacity of supply chain. We propose an empirical law to describe the recent evolution of equipment LR, which shows that the throughput of tool increases 100% in every 3 years, so that the investment in cell production lines has decreased by 50% every 3 years since 2015. Finally, we quantify the material consumption and carbon footprint of PV plants today and for the expansion of PV to terawatt (TW) levels. Besides replacing silver fingers with copper and aluminium, saving copper cables in utilities and low‐carbon mining of materials are the most effective carbon reduction measures in the PV supply chain.

AbstractPotential‐induced degradation‐polarization (PID‐p) can reduce module power, but how to project the extent to which PID‐p may occur in field conditions considering the factors of system voltage, condensed moisture, temperature, and illumination has not been clarified. Using tunnel oxide passivated contact (TOPCon) modules, this work demonstrates a method to test full‐size crystalline silicon PV modules for PID‐p to provide field‐representative results. In initial screening tests with positive or negative 1000 V electrical bias applied at 60°C for 96 h using Al foil electrodes on the glass surfaces, the module type exhibited reversible PID‐p only on the front face when the cell circuit was in negative voltage potential. No PID was detected on the rear after testing in either polarity. We then evaluated the PID‐p sensitivity on the front side under different UV irradiances while maintaining the glass surface wet to estimate real‐world susceptibility to PID‐p. The magnitude of the observed behavior was fit using a previously developed charge transfer and depletion by light model. Whereas power loss with −1000 V applied to the cell circuit at 60°C for 96 h in the dark was about 30%, testing the module front under 0.051 W·m−2 nm−1 at 340 nm UVA irradiation using fluorescent tubes, the mean degradation was only 3%. When the modules were tested in the dark for PID‐p with in situ dark current–voltage (I‐V) characterization, the thermal activation energy for degradation was 0.71 eV; for recovery in the dark, it was 0.58 eV. Whereas recovery from the degraded state at 60°C in the dark without voltage bias was 5% absolute in 38 h, rapid recovery of about 5% absolute was observed with 1000 W·s/m2 exposure at 25°C using a flash tester.

AbstractWe present an industrial tunnel oxide passivated contacts (i‐TOPCon) bifacial crystalline silicon (c‐Si) solar cell based on large‐area n‐type substrate. The interfacial thin SiO2 is thermally growth and in situ capped by an intrinsic poly‐Si layer deposited by low‐pressure chemical vapor deposition (LPCVD). The intrinsic poly‐Si layer is doped in an industrial POCl3 diffusion furnace to form the n+ poly‐Si at the rear, which shows an excellent surface passivation characteristics with J0 = 2.6 fA/cm2 when passivated by a SiNx:H layer deposited by plasma‐enhanced chemical vapor deposition (PECVD). With an industrial fabrication process, the cells are manufactured with screen‐printed front and rear metallization, using large‐area 6‐in. n‐type Czochralski (Cz) Si wafers. We demonstrate an average front‐side efficiency greater than 23% and an open‐circuit voltage Voc greater than 700 mV. These results are based on more than 20 000 pieces of cells from mass production on a single day, in an old conventional multicrystalline silicon (mc‐Si) Al‐back surface field (BSF) cell workshop, which has been upgraded to i‐TOPCon process. The best cell efficiency reaches 23.57%, as independently confirmed by Fraunhofer CalLab. A median module power greater than 345 W and a best module power greater than 355 W are demonstrated with double‐glass bifacial i‐TOPCon modules consisting of 120 pieces of half‐cut 161.7 mm pseudosquare i‐TOPCon cells with nine busbars.