The Application Of Cd₂SSe/ZnS Quantum Dots In Polymer Solar Cells

Recently,polymer solar cells?PSCs?have been one of the most remarkable progresses in energy fields.Among the rest,the inverted polymer solar cells?i-PSCs?have attracted widespread attentions because of the potential advantages in low cost of fabrication,portable carry of flexible material,large area of manufacture with printing technology,and superior photochemical stability of construction.However,it is undeniable that the lower power conversion efficiency?PCE?of PSCs has a serious disadvantage for applicable promotion in comparison with prime inorganic solar cells,which mainly originates from the existent deficiency of the open-circuit voltage(V_oc)associating with band gap?E_g?and the narrow light absorption spectrum of the donor/acceptor?D/A?materials.The novel materials play a vital role on the performance of photovoltaic devices,D/A polymer active layers commendably absorb the photon energy of illumination and realize the exciton generation and charge carrier transport,which are the crucial factor for the short-circuit current(J_sc).Hence,some photo-sensitizers have been doped into active layers to achieve further improvement toward increasing light path and wavelength range in the visible region,leading to a significant enhancement of J_sc.In this work,Cd₂SSe/ZnS?CSS-Z?QDs was blended into the active layers to improve the PCE of thei-PSCs.Poly[N-9?-hepta-decanyl-2,7-carbazolealt-5,5-?4?,7?-di-2-thienyl-2?,1?,3?-ben-zothiadiazole?]?PCDTBT?as electron donor and fullerene derivative[6,6]-phenyl-C70-butyric acid methyl ester(PC₇₁BM)as acceptor(PCDTBT:PC₇₁BM)were applied,with complete device structure of ITO/TiO₂/PCDTBT:PC₇₁BM:CSS-Z QDs/Mo O₃/Ag.After introducing CSS-Z QDs into active layers,the J_sc was improved greatly,while the PCE of i-PSCs increased from 5.72%to 6.75%mostly owing to enhanced photocurrent.Meanwhile,interfacial engineering also fulfills the accomplishment,the interfaces between electrodes and active layers strengthen the charge transport properties between donor and acceptor,triumphantly switching over to more electron-hole pairs and more balancing charge carrier transfer and aggregation.Moreover,the interface morphology and feature also need to be optimized to guarantee the increase of charge transport and fill factor?FF?.In this contribution,the i-PSCs were designed and fabricated by introducing the CSS-Z QDs to modify the polymer polyethylenimine?PEI?buffer layer,which based on poly?3-hexylthiophene??P3HT?donor blending with indene-C60 bisadduct?ICBA?acceptor as active layers.Consequently,the performance of the device was achieved an apparent improvement,and PCE of i-PSCs was increased from 4.15%up to 6.49%for the control device and optimal device,accompanying with 8.63 to 11.84 mA/cm² for J_scc and 56.79%to 65.23%for FF.Undoubtedly,the CSS-Z QDs materials as excellent candidates could achieve prospective performance for i-PSCs,since they have adjustable and prolonged absorption spectra in the visible region,serving as exciton dissociation center and providing permeability channels between the active layers and electrodes,which could effectively promote the exciton diffusion and charge mobility.