Abstract
Minimizing carrier recombination at interfaces is of extreme importance in the development of high-efficiency photovoltaic devices and for bulk material characterization. Here, we investigate a temporary room temperature superacid-based passivation scheme, which provides surface recombination velocities below 1 cm/s, thus placing our passivation scheme amongst state-of-the-art dielectric films. Application of the technique to high-quality float-zone silicon allows the currently accepted intrinsic carrier lifetime limit to be reached and calls its current parameterization into doubt for 1 Ω·cm n-type wafers. The passivation also enables lifetimes up to 65 ms to be measured in high-resistivity Czochralski silicon, which, to our knowledge, is the highest ever measured in Czochralski-grown material. The passivation strategies developed in this work will help diagnose bulk lifetime degradation under solar cell processing conditions and also help quantify the electronic quality of new passivation schemes.
Highlights
E XCELLENT surface passivation of crystalline silicon is essential in the production of solar cells with efficiencies >25% and for accurate measurement of charge carrier diffusion lengths in high-quality substrates
The quality of our surface passivation enables the measurement of lifetimes up to, and possibly beyond, the intrinsic lifetime limit, casting doubt over its currently accepted parameterization [5]
We have demonstrated a very high level of surface passivation by controlling the ambient environment and developing a surface conditioning procedure prior to immersing silicon into a superacid-containing solution
Summary
E XCELLENT surface passivation of crystalline silicon is essential in the production of solar cells with efficiencies >25% and for accurate measurement of charge carrier diffusion lengths in high-quality substrates. Schmidt et al have demonstrated better electronic properties for rear-passivated PEDOT:PSS solar cells, where an emitter saturation current density (Joe) of 80 fA/cm and an implied open-circuit voltage (iVoc) of 690 mV have been reported [13], [14] This was further improved by Zielke et al, who achieved Joe of 46 fA/cm by optimizing the silicon surface treatment prior to the deposition of PEDOT:PSS [15]. Bullock et al have developed an organic passivation method in which silicon wafers are briefly dipped in a nonaqueous bis(trifluoromethane)sulfonimide (TFSI) superacid (SA) solution By this procedure, an upper limit S of 3 and 13 cm/s on n- and p-type silicon are achieved, respectively [17]. We demonstrate the capabilities of the passivation scheme by diagnosing bulk lifetime degradation under standard solar cell processing conditions
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