Suleyman Kudret

The ISOS-3 inter-laboratory collaboration focused on the stability of a variety of organic photovoltaic devices

Seven distinct sets (n ≥ 12) of state of the art organic photovoltaic devices were prepared by leading research laboratories in a collaboration planned at the Third International Summit on Organic Photovoltaic Stability (ISOS-3). All devices were shipped to RISO DTU and characterized simultaneously up to 1830 h in accordance with established ISOS-3 protocols under three distinct illumination conditions: accelerated full sun simulation; low level indoor fluorescent lighting; and dark storage with daily measurement under full sun simulation. Three nominally identical devices were used in each experiment both to provide an assessment of the homogeneity of the samples and to distribute samples for a variety of post soaking analytical measurements at six distinct laboratories enabling comparison at various stages in the degradation of the devices. Over 100 devices with more than 300 cells were used in the study. We present here design and fabrication details for the seven device sets, benefits and challenges associated with the unprecedented size of the collaboration, characterization protocols, and results both on individual device stability and uniformity of device sets, in the three illumination conditions.

Synthesis of ester side chain functionalized all-conjugated diblock copolythiophenes via the Rieke method

Ester-functionalized all-conjugated diblock copolythiophenes are synthesized by an optimized Rieke zinc protocol. These light-harvesting semiconducting electron donor polymers are of high interest in the field of organic photovoltaics as both the block architecture and the (functionalized) side chains play a crucial role in determining the bulk heterojunction active layer blend (nano)morphology and thereby the final polymer solar cell efficiency and lifetime.

Ligand exchange and photoluminescence quenching in organic-inorganic blends poly(3-hexylthiophene) P3HT:PbS

Long alkyl chain ligands such as oleic acid (OLA) which cover the as-prepared PbS nanodots act as an insulating layer that impedes efficient charge transfer in PbS nanodots:polymer hybrid solar cells. The replacement of OLA with tailored ligands of an appropriate chain length is needed to achieve a noticeable enhancement of photovoltaic performance. Several studies have centered on the ligand exchange prior to casting the PbS film1,2,3. However, this post synthesis approach requires careful consideration for the choice of a ligand as clustering of the nanodots has to be avoided. Recently, a new approach that allows direct chemical ligand replacement in a blended mixture of PbS:P3HT has been demonstrated 4,5,6. In this contribution, the latter approach (post-fabrication) was compared with the post-synthesis ligand exchange. We investigated the effect of the ligand exchange processes to the charge separation dynamics in the P3HT:PbS blends by steady-state and time-resolved photoluminescence (PL). Hexanoic acid and acetic acid were used as a short-length ligand for the post fabrication approach while decylamine, octylamine and butylamine were used for the post-synthesis approach. As expected, decreasing the chain length of the ligand led to an increase of the P3HT fluorescence quenching. The absence of enhancement of PbS luminescence due to energy transfer from P3HT and the dependence of the quenching efficiency on the bulkiness of the ligands coating the QDs suggest that the quenching of the P3HT fluorescence is dominated by electron transfer to PbS quantum dots (QDs). In addition, the fluorescence quenching is also less prominent in the P3HT with higher regioregularity (RR) suggesting an enhanced phase separation in the blend due to more densely packed nature of conjugated polymer with higher RR.

Stability and degradation of organic photovoltaics fabricated, aged, and characterized by the ISOS 3 inter-laboratory collaboration

Seven distinct sets (n ≥ 12) of state of the art organic photovoltaic devices were prepared by leading research laboratories in a collaboration planned at the Third International Summit on Organic Photovoltaic Stability (ISOS-3). All devices were shipped to DTU and characterized simultaneously up to 1830 h in accordance with established ISOS-3 protocols under three distinct illumination conditions: accelerated full sun simulation; low level indoor fluorescent lighting; and dark storage with daily measurement under full sun simulation. Three nominally identical devices were used in each experiment both to provide an assessment of the homogeneity of the samples and to distribute samples for a variety of post soaking analytical measurements at six distinct laboratories enabling comparison at various stages in the degradation of the devices. Characterization includes current-voltage curves, light beam induced current (LBIC) imaging, dark lock-in thermography (DLIT), photoluminescence (PL), electroluminescence (EL), in situ incident photon-to-electron conversion efficiency (IPCE), time of flight secondary ion mass spectrometry (TOF-SIMS), cross sectional electron microscopy (SEM), UV visible spectroscopy, fluorescence microscopy, and atomic force microscopy (AFM). Over 100 devices with more than 300 cells were used in the study. We present here design of the device sets, results both on individual devices and uniformity of device sets from the wide range of characterization methods applied at different stages of aging under the three illumination conditions. We will discuss how these data can help elucidate the degradation mechanisms as well as the benefits and challenges associated with the unprecedented size of the collaboration.