Abstract
Colloidal quantum dot solar cells (CQDSCs) based on one-dimensional metal oxide nanowires (NWs) as electron transport layer (ETL) have attracted much attention due to its larger ETL/colloidal quantum dots (CQDs) contact area and longer electron transport length than other structure CQDSCs, such as planar CQDSCs. However, it is known that defect states in NWs would increase the recombination rate because of the high surface area of NWs. Here, the defect species on the ZnO NWs surface which resulted in the surface recombination and SnO2 passivation effects were investigated. Comparing with the solar cells using pristine ZnO NWs, the CQDSCs which based on SnO2 passivated ZnO NWs electrode exhibited a beneficial band alignment to charge separation, and the interfacial recombination at ZnO/CQDs interface was reduced, eventually resulted in a 40% improvement of power conversion efficiency (PCE). Overall, these findings indicate that surface passivation and the reduction of deep level defect in ETLs could contribute to improve the PCE of CQDSCs.
Highlights
Colloidal quantum dots (CQDs) have attracted immense attention due to their applications in the field of optoelectronic devices such as lasers (Hoogland et al, 2006), light-emitting diodes (Wood et al, 2009), and photovoltaic devices due to their bandgap tunability and solution processing (Mcdonald et al, 2005; Nozik et al, 2010; Zhang et al, 2012; Kagan et al, 2016)
It can be clearly seen that the length of ZnO NWs is approximately 1 μm, and the morphology of NWs has no change after SnO2 passivation
It can be found that the average diameter of ZnO NWs is about 40 nm and a thin amorphous SnO2 layer coated the surface of ZnO NWs with a thickness of about 2 nm
Summary
Colloidal quantum dots (CQDs) have attracted immense attention due to their applications in the field of optoelectronic devices such as lasers (Hoogland et al, 2006), light-emitting diodes (Wood et al, 2009), and photovoltaic devices due to their bandgap tunability and solution processing (Mcdonald et al, 2005; Nozik et al, 2010; Zhang et al, 2012; Kagan et al, 2016). In CQDSCs, CQDs work as an active (or a light absorbing) layer, and wide bandgap semiconductors (e.g., ZnO, TiO2, etc.) are employed as an electron transport layer (ETL) In this architecture, a depletion region was formed near the ETL/CQD interface, which plays a very important role in charge separation and extraction (Choi et al, 2009; Willis et al, 2012).
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