Triplet diffusion in singlet exciton fission sensitized pentacene solar cells

Singlet fission sensitized photovoltaics have the potential to surpass the Shockley-Queisser limit for a single-junction structure. We investigate the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction. We model the generation and diffusion of excitons to predict the spectral response. We find the triplet diffusion length in polycrystalline pentacene to be 40 nm. Poly(3-hexylthiophene) between the electrode and pentacene works both to confine triplet excitons and also to transfer photogenerated singlet excitons into pentacene with 30% efficiency. The lower bound for the singlet fission quantum efficiency in pentacene is 180 ± 15%

Multiple-exciton generation in lead selenide nanorod solar cells with external quantum efficiencies exceeding 120.

Multiple-exciton generation-a process in which multiple charge-carrier pairs are generated from a single optical excitation-is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley-Queisser limit. One-dimensional nanostructures, for example nanorods, have been shown spectroscopically to display increased multiple exciton generation efficiencies compared with their zero-dimensional analogues. Here we present solar cells fabricated from PbSe nanorods of three different bandgaps. All three devices showed external quantum efficiencies exceeding 100% and we report a maximum external quantum efficiency of 122% for cells consisting of the smallest bandgap nanorods. We estimate internal quantum efficiencies to exceed 150% at relatively low energies compared with other multiple exciton generation systems, and this demonstrates the potential for substantial improvements in device performance due to multiple exciton generation.NJLKD thanks the Cambridge Commonwealth European and International Trust, Cambridge Australian Scholarships and Mr Charles K Allen for financial support. MLB thanks the German National Academic Foundation (“Studienstiftung”) for financial support. MT thanks the Gates Cambridge Trust, EPSRC and Winton Programme for Sustainability for financial support. F.W.R.R. gratefully thanks financial support from CNPq [Grant number 246050/2012-8]. C.D. acknowledges financial support from the EU [Grant number 312483 ESTEEM2]. This work was supported by the EPSRC [Grant numbers EP/M005143/1, EP/G060738/1, EP/G037221/1] and the ERC [Grant number 259619 PHOTO-EM].This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/ncomms925

Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals.

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.This is the author's accepted manuscript and will be under embargo until the 5th of April 2015. The final version is published by NPG in Nature Materials here: http://www.nature.com/nmat/journal/v13/n11/full/nmat4093.html

A Silicon-Singlet Fission Tandem Solar Cell Exceeding 100% External Quantum Efficiency with High Spectral Stability.

After 60 years of research, silicon solar cell efficiency saturated close to the theoretical limit, and radically new approaches are needed to further improve the efficiency. The use of tandem systems raises this theoretical power conversion efficiency limit from 34% to 45%. We present the advantageous spectral stability of using voltage-matched tandem solar cells with respect to their traditional series-connected counterparts and experimentally demonstrate how singlet fission can be used to produce simple voltage-matched tandems. Our singlet fission silicon-pentacene tandem solar cell shows efficient photocurrent addition. This allows the tandem system to benefit from carrier multiplication and to produce an external quantum efficiency exceeding 100% at the main absorption peak of pentacene.This work is part of the research programme of the Netherlands Organisation for Scientific Research (NWO). The authors acknowledge financial support from the Engineering and Physical Sciences Research Council of the UK (EPSRC) and King Abdulaziz City for Science and Technology (KACST). LMPO acknowledges the Cambridge Home European Scholarship Scheme (CHESS). MT acknowledges the Gates Cambridge Trust and the Winton Program for the Physics of Sustainability

Research data supporting "Multiple-exciton generation in lead selenide nanorod solar cells with external quantum efficiencies exceeding 120%"

Data underlying the figures in this publication.This work was supported by the ERC [grant numbers EP/M005143/1, EP/G060738/1, EP/G037221/1] and EPSRC [grant numbers 259619 PHOTO-EM, 312483 ESTEEM2]

Research data supporting "Lead Telluride Quantum Dot Solar Cells Displaying External Quantum Efficiencies Exceeding 120%"

The data is the basis for all Figures in the manuscript and Supporting Information.This work was supported by the ERC [grant numbers 259619 PHOTO-EM,312483 ESTEEM2], EPSRC [grant numbers EP/M005143/1, EP/G060738/1, EP/G037221/1], and the CNPq [grant number 246050/2012-8]

Research data supporting "Efficient singlet exciton fission in pentacene prepared from a soluble precursor"

Underlying datasets for all figures in the Manuscript and the SI. Data comprises results from absorption-, photoluminescence-, ellipsometry-, transient spectroscopy-, FTIR-, X-ray and atomic force microscopy measurements

Solution-Processable Singlet Fission Photovoltaic Devices

We demonstrate the successful incorporation of a solution-processable singlet fission material, 6,13-bis­(triisopropylsilylethynyl)­pentacene (TIPS-pentacene), into photovoltaic devices. TIPS-pentacene rapidly converts high-energy singlet excitons into pairs of triplet excitons via singlet fission, potentially doubling the photocurrent from high-energy photons. Low-energy photons are captured by small-bandgap electron-accepting lead chalcogenide nanocrystals. This is the first solution-processable singlet fission system that performs with substantial efficiency with maximum power conversion efficiencies exceeding 4.8%, and external quantum efficiencies of up to 60% in the TIPS-pentacene absorption range. With PbSe nanocrystal of suitable bandgap, its internal quantum efficiency reaches 170 ± 30%

Research data supporting "Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Nanocrystals"

The uploaded data is the basis for all figures presented in the manuscript and the Supporting InformationThis research data supports “Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Nanocrystals” which has been published in “Journal of the American Chemical Soceity”.This work was supported by the EPSRC [grant numbers EP/261 M005143/1, EP/G060738/1 and EP/G037221/1], Royal Society, Winton Program for the Physics of Sustainability and Gates Cambridge Trust