The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications
<p>This thesis examines the effect of lead sulphide (PbS) CQDs’ surface chemistry and interfaces to their photovoltaic performance. </p> <p>Using PbS CQDs as the starting material, cation-exchange was utilised to form PbS/CdS core/shell CQDs, which were thoroughly characterised and...
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| स्वरूप: | थीसिस |
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2016
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| _version_ | 1826316348131639296 |
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| author | Neo, D |
| author2 | Watt, A |
| author_facet | Watt, A Neo, D |
| author_sort | Neo, D |
| collection | OXFORD |
| description | <p>This thesis examines the effect of lead sulphide (PbS) CQDs’ surface chemistry and interfaces to their photovoltaic performance. </p> <p>Using PbS CQDs as the starting material, cation-exchange was utilised to form PbS/CdS core/shell CQDs, which were thoroughly characterised and the improved surface passivation was shown by increased photoluminescence yield and lifetime. The core/shell CQDs were incorporated into a ZnO/CQD heterojunction solar cell device and showed a substantial improvement of the mean open-circuit voltage (Voc), from 0.4 V to 0.6 V, over PbS reference devices. By optimising shell thickness and surface ligands, core/shell CQD devices with average device efficiency of 5.6 % were fabricated as compared to 3.0 % for unshelled PbS devices.</p> <p>The lower defect density due to better passivation confers lower carrier density in core/shell CQD film. To take advantage of low defect concentration and to aid charge extraction, a 3 dimensional quantum funnel concept was sought of by blending two populations of PbS/CdS CQDs of different sizes. By incorporating a blend component within a heterojunction device, even when the device thickness is beyond what is optimal for the depletion width and the diffusion length of the system, high Voc is still maintained. In a separate study, a p-i-n device strategy was examined, and with this approach, a maximum device efficiency of 6.4 % was achieved. </p> <p>Despite the improvements made to Voc by optimizing surface passivation, fill factors of the devices are low. By using poly(3-hexylthiophene-2,5-diyl) (P3HT) as a hole transport material (HTM), fill factor and the overall performance improved over a reference device without the HTM. Further studies showed that oxidation of the HTM material results in increased p-type characteristic, thus optimising hole transport. This beneficial oxidation process also makes the device air-stable. From this, devices of up to 8.1 % efficiency and devices with fill factor as high as 0.72 were fabricated.</p> |
| first_indexed | 2024-03-06T20:58:42Z |
| format | Thesis |
| id | oxford-uuid:3a23c635-992b-4e46-94d6-72c2aea61ce9 |
| institution | University of Oxford |
| last_indexed | 2024-12-09T03:43:34Z |
| publishDate | 2016 |
| record_format | dspace |
| spelling | oxford-uuid:3a23c635-992b-4e46-94d6-72c2aea61ce92024-12-07T14:43:16ZThe surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applicationsThesishttp://purl.org/coar/resource_type/c_db06uuid:3a23c635-992b-4e46-94d6-72c2aea61ce9ORA Deposit2016Neo, DWatt, AAssender, H<p>This thesis examines the effect of lead sulphide (PbS) CQDs’ surface chemistry and interfaces to their photovoltaic performance. </p> <p>Using PbS CQDs as the starting material, cation-exchange was utilised to form PbS/CdS core/shell CQDs, which were thoroughly characterised and the improved surface passivation was shown by increased photoluminescence yield and lifetime. The core/shell CQDs were incorporated into a ZnO/CQD heterojunction solar cell device and showed a substantial improvement of the mean open-circuit voltage (Voc), from 0.4 V to 0.6 V, over PbS reference devices. By optimising shell thickness and surface ligands, core/shell CQD devices with average device efficiency of 5.6 % were fabricated as compared to 3.0 % for unshelled PbS devices.</p> <p>The lower defect density due to better passivation confers lower carrier density in core/shell CQD film. To take advantage of low defect concentration and to aid charge extraction, a 3 dimensional quantum funnel concept was sought of by blending two populations of PbS/CdS CQDs of different sizes. By incorporating a blend component within a heterojunction device, even when the device thickness is beyond what is optimal for the depletion width and the diffusion length of the system, high Voc is still maintained. In a separate study, a p-i-n device strategy was examined, and with this approach, a maximum device efficiency of 6.4 % was achieved. </p> <p>Despite the improvements made to Voc by optimizing surface passivation, fill factors of the devices are low. By using poly(3-hexylthiophene-2,5-diyl) (P3HT) as a hole transport material (HTM), fill factor and the overall performance improved over a reference device without the HTM. Further studies showed that oxidation of the HTM material results in increased p-type characteristic, thus optimising hole transport. This beneficial oxidation process also makes the device air-stable. From this, devices of up to 8.1 % efficiency and devices with fill factor as high as 0.72 were fabricated.</p> |
| spellingShingle | Neo, D The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| title | The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| title_full | The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| title_fullStr | The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| title_full_unstemmed | The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| title_short | The surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| title_sort | surface chemistry and interface engineering of lead sulphide colloidal quantum dots for photovoltaic applications |
| work_keys_str_mv | AT neod thesurfacechemistryandinterfaceengineeringofleadsulphidecolloidalquantumdotsforphotovoltaicapplications AT neod surfacechemistryandinterfaceengineeringofleadsulphidecolloidalquantumdotsforphotovoltaicapplications |