The current solar energy marketplace is dominated by silicon; however, the efficiency of these cells is substantially hampered by silicon’s poor ability to absorb energy below its bandgap at 1.14 eV. A process called photon upconversion, that uses pairs of incoherent, low-energy photons to produce higher energy photons, can combat this issue by converting the sun’s infrared rays into light that can be absorbed by silicon. However, an efficient system that can upconvert infrared to visible light for this purpose remains elusive. To address this need, we have investigated perylenediimide (PDI) molecules that have been attached to the surface of lead sulfide (PbS) quantum dots as a potential system of infrared upconversion. Upon low-energy excitation of a PbS quantum dot, it can pass its energy to an interfaced PDI molecule, placing the molecule into a dark, spin-triplet excited state. Pairs of these triplet-excited molecules can subsequently pool their energy to form a high-energy, emissive spin-singlet state. Using ultrafast transient absorption, we investigated the photoexcited dynamics of this system in solution, expecting to observe triplet formation based on the energetic alignment of PDI and PbS electronic states. Instead, we saw single electron transfer from PbS to PDI at an intrinsic rate of ~30 ps, evidenced by the formation of PDI anions. Importantly, we found that by tuning the energy levels of the PbS quantum dots relative to vacuum by attaching cinnamate ligands with large dipole moments to their surface, we can adjust the PbS-to-PDI electron transfer rate by nearly an order of magnitude. Our findings indicate that by changing the relative energy levels between PbS and PDI in our complex, heterogeneous system, we can selectively modify the PbS:PDI interface towards favoring either charge or energy transfer. This widely diversifies the range of applications that our system could potentially address, from upconversion via triplet formation to catalysis via excited anion formation. Furthermore, our work highlights the importance of considering relative energy levels when designing inorganic:organic interfaces for triplet energy and/or charge transfer, which we believe will guide future efforts to design high-efficiency light harvesting technologies.

Manipulating energy transfer at the surface of PbS nanocrystals

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.