High efficiency inline diffused emitter (ILDE) solar cells on mono‐crystalline CZ silicon

Abstract

High throughput, low cost, and high efficiency are the keys to reducing the cost of photovoltaic electricity. To realize high efficiency, the quality of emitter is critical. The emitter can be formed either by batch deposition in a tube using liquid POCl 3 source or by inline spray deposition of phosphoric acid (P 2 O 5 ). The POCl 3 process has been optimized over the years to give reproducible performance, whereas the inline diffusion has not been systematically optimized. This paper reports on solar cell results with the inline emitters. Sheet resistance mapping tool has been used to quantify the emitter uniformity in conjunction with junction depth and phosphorus surface concentration to characterize the inline emitters. We have achieved average efficiencies of 17.1 and 17.4%, respectively, on 2 V-cm textured CZ with 45 and 60 V/sq emitters. Average fill factor of 0.772 and ideality factor of 1.06 support the front contact firing optimization for the inline emitters. Personal computer one dimensional (PC1D) modeling of the 60 V/sq emitter showed efficiency of >18% is achievable by reducing the front surface recombination velocity (FSRV) from 120 000 to 80 000 cm/s and increasing the fill factor to 79.5%.

Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

“…Ebong et al observed an increase in phosphorus emitter sheet resistance and decrease in surface doping concentration after an HF dip, which indicated that considerable amount of Si was removed in the solution [15]. Liu et al studied the topic further and discovered that phosphorus concentration affects the etch rate of Si in HF.…”

0.4% absolute efficiency increase for inline-diffused screen-printed multicrystalline silicon wafer solar cells by non-acidic deep emitter etch-back

“…An absolute efficiency gain of 0.2-0.3% with a moderate increase in emitter R sq (i.e., ΔR sq ) of 6 Ω/sq was reported when using this 'surface clean' [11]. Ebong et al [3] reported an 'extended surface clean' process and achieved an average efficiency of 17.4% for ILDE mono-Si wafer cells. Using an inline diffusion furnace with ceramic rollers and 'augmented clean' emitter etch-back process, Rousenville et al [12] reported a champion efficiency of 18.2% for mono-Si solar cells featuring a plated Ag front metallization (using a screen-printed Ag seed layer).…”

“…As a result, processing conditions must be chosen to address these impacts, otherwise typical cell efficiency of an inline-diffused emitter (ILDE) Si solar cells can be lower compared to their tube-diffused counterpart. A surface 'dead layer' can be formed on the ILDE surface by a high dopant concentration at the surface and surface contaminants resulting from direct deposition of dopants on the wafers [2,3]. This dead layer directly limits short-circuit current (I sc ) and open-circuit voltage (V oc ) of the solar cell [3][4][5].…”

“…Several research groups have applied different surface etching or cleaning processes to remove the dead layer (along with SiP precipitates) [3,7,8,[10][11][12][13] and these 'cleaning' or 'etching' processes for the emitters are commonly known as emitter etch-back processes. A surface treatment by the solution of nitric acid (HNO 3 ) and HF was used on an ILDE surface by Voyer et al [10] on mono-Si wafers.…”

“…A surface 'dead layer' can be formed on the ILDE surface by a high dopant concentration at the surface and surface contaminants resulting from direct deposition of dopants on the wafers [2,3]. This dead layer directly limits short-circuit current (I sc ) and open-circuit voltage (V oc ) of the solar cell [3][4][5]. Also the short duration of the diffusion process affords less impurity gettering and this can limit the V oc and efficiency of ILDE solar cells [6,7].…”