Engineering the Temporal Response of Photoconductive Photodetectors via Selective Introduction of Surface Trap States

Abstract

Photoconductive photodetectors fabricated using simple solution-processing have recently been shown to exhibit high gains (>1000) and outstanding sensitivities ( D* > 10(13) Jones). One ostensible disadvantage of exploiting photoconductive gain is that the temporal response is limited by the release of carriers from trap states. Here we show that it is possible to introduce specific chemical species onto the surfaces of colloidal quantum dots to produce only a single, desired trap state having a carefully selected lifetime. In this way we demonstrate a device that exhibits an attractive photoconductive gain (>10) combined with a response time ( approximately 25 ms) useful in imaging. We achieve this by preserving a single surface species, lead sulfite, while eliminating lead sulfate and lead carboxylate. In doing so we preserve the outstanding sensitivity of these devices, achieving a specific detectivity of 10(12) Jones in the visible, while generating a temporal response suited to imaging applications.

Solution-processed semiconductors for next-generation photodetectors

“…Although sufficient for most imaging applications, this gain-bandwidth product limitation represents a significant drawback for higher speed applications such as in-flight object recognition. 45,46 Further improvements in CQD films to address their most acute limitation, i.e. mobility, has led to the realization of faster photoconductive responses (0.4 kHz bandwidth) with high internal gain (G > 6.5·10 3 ) and detectivity (D* ~ 10 13 Jones).…”

Ethanedithiol Treatment of Solution‐Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics

“…We note that the EDT treatment has previously been demonstrated to be effective in terms of replacing the original long-chain insulating ligands of lead chalcogenide or cadmium chalcogenide based quantum dots, and the EDT treatment leads to improved inter-particle electronic coupling and enhanced charge transport properties of the quantum dot based films. [24][25][26][27][28][29] Fourier transform infrared spectroscopy (FTIR) analyses on the P-ZnO films reveal the presence of hydroxyl groups and carboxylate groups. As shown in Figure 1a, the broad peak at 3390 cm -1 corresponds to the hydroxyl groups and the peaks at 1560 and 1420 cm -1 correspond to the carboxylate groups.…”

Photovoltaic Devices Employing Ternary PbSxSe1-x Nanocrystals

“…22,26,27 We hypothesize that the better performance of ternary nanocrystals is due to a combination of material properties as well as a redistribution of the trap states. The higher current produced by PbS x Se 1-x , may arise from a significantly larger exciton Bohr radius than PbS due to the incorporation of Se (46nm for PbSe and 18nm for PbS).…”