Charge generation and energy transfer in hybrid polymer/infrared quantum dot solar cellsElectronic supplementary information (ESI) available: Includes PPEHTT synthesis, cyclic voltammograms of the three polymers, photoinduced spectroscopy measurements on (1) neat quantum dots, (2) polymer/fullerene blends, and (3) PSOTT/quantum dot blend compared against a sample of neat PSOTT, a schematic diagram of PSOTT/PbS Schottky diode, EQE data from a PSOTT/PbS device that did not undergo post-film ligand

Conjugated polymers blended with nanocrystal quantum dots are interesting as solution processable active layers for infrared light harvesting in thin film solar cells. We study photocurrent generation processes in hybrid polymer/quantum dot photovoltaics by comparing device performance and photoinduced absorption (PIA) spectra across blends of three different conjugated polymers, poly(2,3-bis(2-(hexyldecyl)-quinoxaline-5,8-diyl- alt-N -(2-hexyldecyl)-dithieno[3,2- b :2′,3′- d ]pyrrole) (PDTPQx-HD), poly[(4,4′-bis(3-(2-hexyl-decyl)dithieno[3,2- b :2′,3′- d ]pyrrole)-2,6-diyl- alt -(2,5-bis(3-(2-ethyl-hexyl)thiophen-2yl)thiazolo[5,4- d ]thiazole)] (PPEHTT), and poly[(4,4′-bis(2-octyl)dithieno[3,2- b :2′3′- d ]silole)-2,6-diyl- alt -(2,5-bis(3-octylthiophen-2yl)thiazolo[5,4- d ]thiazole)] (PSOTT) with PbS quantum dots. The PIA spectra and device performance provide evidence for long-lived photoinduced charge separation and bulk heterojunction device operation for blends of both PDTPQx-HD and PPEHTT with PbS. In contrast we find that PSOTT/PbS blends can produce viable solar cells without any evidence for long-lived charge transfer in the PIA spectra. Even so, the external quantum efficiency (EQE) spectra of PSOTT/PbS solar cells indicate that the polymer plays a significant role in light harvesting. We use photoluminescence excitation spectroscopy to confirm that the polymer funnels energy to the PbS quantum dots via energy transfer, and speculate that these blends may operate as PbS Schottky diodes sensitized by energy transfer from the semiconducting polymer host. We observe both charge transfer and energy transfer in different hybrid polymer/quantum dot PbS quantum dot solar cells.