Any new solar photovoltaic (PV) technology must reach low production costs to compete with today's marketleading crystalline silicon and commercial thin-film PV technologies. Colloidal quantum dots (QDs) could open up new applications by enabling lightweight and flexible PV modules. However, the cost of synthesizing nanocrystals at the large scale needed for PV module production has not previously been investigated. Based on our experience with commercial QD scale-up, we develop a Monte Carlo model to analyze the cost of synthesizing lead sulfide and metal halide perovskite QDs using 8 different reported synthetic methods. We also analyze the cost of solution-phase ligand exchange for preparing deposition-ready PbS QD inks, as well as the manufacturing cost for roll-to-roll solution-processed PV modules using these materials. We find that present QD synthesis costs are prohibitively high for PV applications, with median costs of 11 to 59 $ per g for PbS QDs (0.15 to 0.84 $ per W for a 20% efficient cell) and 73 $ per g for CsPbI 3 QDs (0.74 $ per W). QD ink preparation adds 6.3 $ per g (0.09 $ per W). In total, QD materials contribute up to 55% of the total module cost, making even roll-to-roll-processed QDPV modules significantly more expensive than silicon PV modules. These results suggest that the development of new low-cost synthetic methods is critically important for the commercial relevance of QD photovoltaics. Using our cost model, we identify strategies for reducing synthetic cost and propose a cost target of 5 $ per g to move QD solar cells closer to commercial viability.
Broader contextColloidal quantum dots (QDs) have been widely investigated as an avenue toward ultra-low-cost solar photovoltaics (PV), alongside organics and metal halide perovskites. It is often implicitly assumed-and explicitly stated-that QD-based PV technologies can reach low cost because they employ low-cost, abundant elements and low-temperature, high-throughput manufacturing processes. However, this argument holds true only if QDs can be synthesized at low cost-materials dictate the module cost floor. Here we report the first detailed analysis of the cost of large-scale QD synthesis for PV applications. Our Monte Carlo approach constitutes a complete cost modeling framework for QD photovoltaics, from raw precursors to finished modules. We find that QD synthesis is prohibitively expensive today, highlighting the importance of synthetic cost for the commercial viability of QD solar technologies and guiding further research toward promising synthetic directions.
Semiconductor nanostructures have shown promise for light emission across various intensity regimes. Desired performance objectives of photoluminescence efficiency, low gain threshold, large gain lifetime and bandwidth have not been met by any one nanocrystal. A physical understanding of the design principles governing these objectives is also lacking. We show that a carefully engineered CdSe/Cd,Zn,S core/shell nanocrystal uniquely meets all criteria. The key factor allowing for these improvements is the gradual core/shell boundary, which decouples the surface electronic states.
The interface of semiconductor nanocrystals is a critical factor for determining their performance in light emissive applications. Traditional nanocrystals have an abrupt termination of the core/shell interface. Recent synthetic work has focused upon developing graded core/shell interfaces via alloying. Here, we employ femtosecond stateresolved pump/probe spectroscopy, temperature-dependent photoluminescence spectroscopy, and a microscopic theory of interfacial charge trapping to reveal the manner in which a graded interface controls the main optical gain metrics: threshold, bandwidth, and lifetime in the CdSe/Cd,Zn,S core/shell system. Photoluminescence spectroscopy in conjunction with semiclassical electron transfer theory reveals the absence of an interfacial electronic state. This absence of a surface/interfacial state is unique to these nanocrystals with a graded shell structure, enabling trap free performance. Excitonic state-resolved pump/probe spectroscopy reveals that the higher excitons do not have the same symmetries as spherical CdSe nanocrystals, thereby enabling increased bandwidth. These pump/probe experiments further reveal the unique electronic structure of the band-edge biexciton which enables single exciton gain in these nanocrystal systems. Finally, the long gain lifetimes are discussed in light of the absence of a surface/interfacial electronic state. These experiments provide the first direct view of how interfacial electronic structure can be probed and understood so as to optimize their performance for light emission and optical gain for the metrics of threshold, bandwidth, and lifetime.
Semiconductor
nanocrystals are being developed with increasingly
complex shapes and geometries, often featuring complex shell structures.
One aims to characterize these structures by different probes, beyond
electronic spectroscopies. Vibrational spectroscopy is a useful tool
to probe the phononic structure, but the commonly used frequency-domain
methods can be plagued by artifacts due to charge-trapping dynamics.
To circumvent these issues, coherent phonons may be measured in the
time domain via excitonic state-resolved pump/probe spectroscopy.
These measurements reveal several new observations on phononic processes,
focusing on model systems of radially graded alloys of core/shell
nanocrystals: CdSeCd
X
Zn1–X
S. The main new observation is frequency changes
to the longitudinal optical phonon at high energy due to electronic
mixing. This new, softened phonon mode appears via previously unobserved
biexcitonic signals. The state-resolved measurements reveal insights
into how the shelling process controls excitonic polarization, carrier
trapping, and perturbations to sphericity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.