Rear Passivated Silicon Solar Cells Research Articles

A solid strategy to realize heteroface selective emitter and rear passivated silicon solar cells

AbstractPassivated emitter and rear cell (PERC) with laser‐doped selective emitter (SE) has become mainstream in the PV industry. In this work, we report a solid strategy to realize heteroface monocrystalline silicon (mono‐Si) wafers for PERC‐SE solar cells by employing alkaline polishing to form a polished surface for the rear side and well‐established metal‐catalyzed chemical etching to form a honeycomb texture for the front side in one wet process successively. The key to success lies in the fact that the two back‐to‐back wafers inserted into one slot in the cassette are tightly attached together in MCCE etching so that only the exposed surfaces are etched to form textures, while the rear polished surfaces are still retained to avoid wrap‐around etching. With the strategy, the mono‐Si PERC‐SE solar cells achieve an average efficiency of over 22.0%, no poorer than that of the reference system (traditional alkaline texturing and rear acidic polishing), and have good light trapping capability for oblique incident light. Moreover, the total Si removal in the novel process is only ~0.4 g, which is far less than that in the traditional process. More importantly, the strategy can also double the throughput of existing texturing processes and significantly reduce the amount of etching waste. Therefore, the work is expected to provide a promising way to mass produce efficient mono‐Si PERC‐SE solar cells with a superior rear surface, achieved without increasing the number of processing steps, and lower cost.

A Systematic Loss Analysis Method for Rear-Passivated Silicon Solar Cells

By combining commonly available solar cell characterization methods with easy-to-prepare test structures and partially processed rear-passivated solar cells from the production line, we show that various cell loss mechanisms can be quantified in exquisite detail to generate process-related diagnostics. An example monocrystalline silicon localized back surface field solar cell type is examined using a systematic routine that breaks down the factors limiting open-circuit voltage, short-circuit current, and fill factor (FF) to identify the cell structure's headroom for improvement.

High-Efficiency Large-Area Rear Passivated Silicon Solar Cells With Local Al-BSF and Screen-Printed Contacts

This paper describes the cell design and technology on large-area (239 cm2) commercial grade Czochralski Si wafers using industrially feasible oxide/nitride rear passivation and screen-printed local back contacts. A combination of optimized front and back dielectrics, rear surface finish, oxide thickness, fixed oxide charge, and interface quality provided effective surface passivation without parasitic shunting. Increasing the rear oxide thickness from 40 to 90 A in conjunction with reducing the surface roughness from 1.3 to 0.2 μm increased the Voc from 640 mV to 656 mV. Compared with 18.6% full aluminum back surface field (Al-BSF) reference cell, local back-surface field (LBSF) improved the back surface reflectance (BSR) from 65% to 93% and lowered the back surface recombination velocity (BSRV) from 310 to 130 cm/s. Two-dimensional computer simulations were performed to optimize the size, shape, and spacing of LBSF regions to obtain good fill factor (FF). Model calculations show that 20% efficiency cells can be achieved with further optimization of local Al-BSF cell structure and improved screen-printed contacts.

Open-circuit voltages: Theoretical and experimental optimizations of rear passivated silicon solar cells using Fz and Cz wafers

The theoretical and experimental open-circuit voltage optimizations of a simple fabrication process of silicon solar cells n + p with rear passivation are presented. The theoretical results were obtained by using an in-house developed program, including the light trapping effect and metal-grid optimization. On the other hand, the experimental steps were monitored by the photoconductive decay technique. The starting materials presented thickness of about 300 μm and resistivities: FZ (0.5 Ω cm), Cz-type 1 (2.5 Ω cm) and Cz-type 2 (3.3 Ω cm). The Gaussian profile emitters were optimized with sheet resistance between 55 Ω/sq and 100 Ω/sq, and approximately 2.0 μm thickness in accordance to the theoretical results. Excellent implied open-circuit voltages of 670.8 mV, 652.5 mV and 662.6 mV, for FZ, Cz-type 1 and Cz-type 2 silicon wafers, respectively, could be associated to the measured lifetimes that represents solar cell efficiency up to 20% if a low cost anti-reflection coating system, composed by random pyramids and SiO 2 layer, is considered even for typical Cz silicon.