Abstract
Roll-to-roll (R2R) device fabrication using solution-processed materials is a cheap and versatile approach that has attracted widespread interest over the past 2 decades. Here, we systematically introduce and investigate R2R-friendly modifications in the fabrication of ultrathin, sintered CdTe nanocrystal (NC) solar cells. These include (1) scalable deposition techniques such as spray-coating and doctor-blading, (2) a bath-free, controllable sintering of CdTe NCs by quantitative addition of a sintering agent, and (3) radiative heating with an infrared lamp. The impact of each modification on the CdTe nanostructure and solar cell performance was first independently studied and compared to the standard, non-R2R-friendly procedure involving spin-coating the NCs, soaking in a CdCl2 bath, and annealing on a hot plate. The R2R-friendly techniques were then combined into a single, integrated process, yielding devices that reach 10.4% power conversion efficiency with a Voc, Jsc, and FF of 697 mV, 22.2 mA/cm2, and 67%, respectively, after current/light soaking. These advances reduce the barrier for large-scale manufacturing of solution-processed, ultralow-cost solar cells on flexible or curved substrates.
Highlights
Solution-processed solar cells assembled from roll-to-roll (R2R)-friendly techniques have garnered increasing interest over the past few decades as a low-cost alternative to single crystal silicon or chemical vapor-deposited gallium arsenide thin films.[1]
The CdTe layer was deposited via a layer-by-layer method using pyridine-capped CdTe NCs, soaking in a CdCl2 bath, and annealing on a hot plate. (d) Schematic of the standardized device architecture (ITO/CdTe/zinc oxide (ZnO):In/Al). (e) J−V curves and power conversion efficiencies (PCEs) for devices fabricated by spin-coating, doctor-blading, or spray-coating after current/light soaking
Using a homebuilt spray-coating system (Figure S1), we tested the spray-coating deposition method by starting with pyridine-capped CdTe NCs previously described by Jasieniak et al.[17] and Panthani et al.[29]
Summary
Solution-processed solar cells assembled from roll-to-roll (R2R)-friendly techniques have garnered increasing interest over the past few decades as a low-cost alternative to single crystal silicon or chemical vapor-deposited gallium arsenide thin films.[1]. Panthani et al and MacDonald et al improved the n-type contact to a p-CdTe absorber using In-doped sol−gel ZnO.[29,30] They found that current/light soaking significantly improved the contact between CdTe and ITO Both reports employed a saturated cadmium chloride (CdCl2) bath as a critical chemical treatment for achieving high PCEs. both reports employed a saturated cadmium chloride (CdCl2) bath as a critical chemical treatment for achieving high PCEs This CdCl2 bath step is not R2R-friendly because it wastes large quantities of CdCl2, which is an expensive, highly toxic, and difficult-todispose of chemical.[31] in order to prevent castatrophic device failure, the bath step requires an extensive washing step to remove CdCl2 particulates from the substrate. We showed that these modifications can be seamlessly integrated to produce a completely R2R-friendly fabrication of the CdTe layer, producing solar cells that perform comparably to those made with non-R2R-friendly techniques
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