Aqueous-Processed Inorganic Thin-Film Solar Cells Based on CdSe_xTe_1–x Nanocrystals: The Impact of Composition on Photovoltaic Performance

Abstract

Aqueous processed nanocrystal (NC) solar cells are attractive due to their environmental friendliness and cost effectiveness. Controlling the bandgap of absorbing layers is critical for achieving high efficiency for single and multijunction solar cells. Herein, we tune the bandgap of CdTe through the incorporation of Se via aqueous process. The photovoltaic performance of aqueous CdSexTe1-x NCs is systematically investigated, and the impacts of charge generation, transport, and injection on device performance for different compositions are deeply discussed. We discover that the performance degrades with the increasing Se content from CdTe to CdSe. This is mainly ascribed to the lower conduction band (CB) of CdSexTe1-x with higher Se content, which reduces the driving force for electron injection into TiO2. Finally, the performance is improved by mixing CdSexTe1-x NCs with conjugated polymer poly(p-phenylenevinylene) (PPV), and power conversion efficiency (PCE) of 3.35% is achieved based on ternary NCs. This work may provide some information to further optimize the aqueous-processed NC and hybrid solar cells.

Impedance Spectroscopy: A Versatile Technique to Understand Solution‐Processed Optoelectronic Devices

“…Since the sandwich‐like device configuration ensures polymer solar cell works as a photodiode, the charge transferring, and accumulation process is related to resistance and capacitance of the device, respectively, which means one can propose an equivalent circuit of resistance and capacitance in series or parallel to describe the work situation of the polymer solar cell. In that case, IS is undoubtedly an easy and direct way to investigate the interfacial process of polymer solar cells …”

Hybrid Solar Cells from Aqueous Polymers and Colloidal Nanocrystals

“…To tune the bandgap of CdTe for better performance, we synthesized CdTe NCs incorporation of Se. [85] As shown in Figure 8a, by changing the content of Se, the bandgaps of CdSe x Te 1x NCs were changed. However, the CB levels lowered heavily along with the increasing of Se content, leading to a hindered electron injection from CdSe x Te 1x NCs to the electron transport layer (ETL), thus decreasing the PV performance.…”

“…Finally, a record PCE of 2.14% was obtained, which was the highest for water-based material HSCs at that time, with a J sc of 10.7 mA/cm 2 , V oc of 0.5 V and FF of 0.4. After that, various efforts have been made to improve the performance of the aqueous HSCs, including synthesizing aqueous polymers [70,76,[80][81][82][83] and NCs [71,72,84,85] with different bandgaps and energy levels, optimizing the device structure as well as the charge transport layers, [39,74,75,86] and studying the working junction and mechanism. [87][88][89] The PCE has increased a lot, however, it is still far from satisfaction.…”

Recent Progress on Solution-Processed CdTe Nanocrystals Solar Cells

“…Alloy NCs were also used as acceptors for HSCs. Cd 0.75 Hg 0.25 Te [77] colloid quantum dots (CQDs) and CdSe x Te 1¡x NCs [78] were introduced into a water-soluble conjugated polymer to extend the spectrum response in near infrared for HSC. In order to increase the miscibility between polymers and aqueous CdTe NCs, water-soluble MEH-PPV precursor was used as a donor material for HSC.…”