The role of electron-hole recombination in organic magnetoresistance

Magneto-electrical measurements were performed on diodes and bulk heterojunction solar cells (BHSCs) to clarify the role of formation of coulombically bound electron-hole (e-h) pairs on the magnetoresistance (MR) response in organic thin film devices. BHSCs are suitable model systems because they effectively quench excitons but the probability of forming e-h pairs in them can be tuned over orders of magnitude by the choice of material and solvent in the blend. We have systematically varied the e-h recombination coefficients, which are directly proportional to the probability for the charge carriers to meet in space, and found that a reduced probability of electrons and holes meeting in space lead to disappearance of the MR. Our results clearly show that MR is a direct consequence of e-h pair formation. We also found that the MR line shape follows a power law-dependence of B0.5 at higher fields

The Effect of Degradation on the Active Layer in APFO3: PCBM Solar Cells

AbstractWe have measured the effect of degradation on the I-V characteristics in APFO3:PCBM solar cells. The solar cell devices were subject to ambient air under simulated solar illumination. We found that the degradation resulted in a lowering of the fill factor and short circuit current while the open circuit voltage remained unchanged. In order to gain insight into what has caused the degraded I-V characteristics we have studied the active layer film using various techniques. We found clear spectral changes both in absorption and in photoinduced absorption spectroscopy correlated with increased carrier lifetimes and lowered mobility when comparing the degraded film with a pristine one. The results show a significant degradation of the active layer causing a lower fill-factor and short circuit current

Lääkeneuvonnan ja potilaille suunnatun kirjallisen lääkeinformaation vaikuttavuus: katsaus

English summaryPeer reviewe

Mortality and cause of death in hip fracture patients aged 65 or older - a population-based study

<p>Abstract</p> <p>Background</p> <p>The high mortality of hip fracture patients is well documented, but sex- and cause-specific mortality after hip fracture has not been extensively studied. The purpose of the present study was to evaluate mortality and cause of death in patients after hip fracture surgery and to compare their mortality and cause of death to those in the general population.</p> <p>Methods</p> <p>Records of 428 consecutive hip fracture patients were collected on a population-basis and data on the general population comprising all Finns 65 years of age or older were collected on a cohort-basis. Cause of death was classified as follows: malignant neoplasms, dementia, circulatory disease, respiratory disease, digestive system disease, and other.</p> <p>Results</p> <p>Mean follow-up was 3.7 years (range 0-9 years). Overall 1-year postoperative mortality was 27.3% and mortality after hip fracture at the end of the follow-up was 79.0%. During the follow-up, age-adjusted mortality after hip fracture surgery was higher in men than in women with hazard ratio (HR) 1.55 and 95% confidence interval (95% CI) 1.21-2.00. Among hip surgery patients, the most common causes of death were circulatory diseases, followed by dementia and Alzheimer's disease. After hip fracture, men were more likely than women to die from respiratory disease, malignant neoplasm, and circulatory disease. During the follow-up, all-cause age- and sex-standardized mortality after hip fracture was 3-fold higher than that of the general population and included every cause-of-death category.</p> <p>Conclusion</p> <p>During the study period, the risk of mortality in hip fracture patients was 3-fold higher than that in the general population and included every major cause of death.</p

Photoexcitation dynamics in organic solar cell donor/acceptor systems

Solceller presenteras ofta som ett miljövänligt alternativ för energiproduktion. Det största hindret för en bredare ibruktagning av kiselbaserade solceller är deras höga pris. I och med upptäckten av ledande och halvledande organiska (kolbaserade) molekyler och polymerer har ett nytt forskningsområde, organisk elektronik, vuxit fram. Den stora fördelen med organisk elektronik är att de använda materialen oftast är lösliga. Tillverkning av elektroniska komponenter kan då göras med hjälp av konventionella trycktekniker där bläcket ersatts med upplösta organiska material. Detta har potential att betydligt sänka priset för solceller. Nackdelen med organisk elektronik är att de använda materialen är komplexa, och de fysikaliska processerna i dem likaså. I min avhandling har jag studerat fotofysiken i två polymerer, P3HT och APFO3, som kan användas för att tillverka organiska solceller. Blandade med fullerenderivatet PCBM, som är en stark elektronacceptor, fås ett material som effektivt producerar elektroner och hål under belysning. I praktiken bidrar dock inte alla skapade laddningar till strömmen ur solcellen. Elektronerna och hålen kan förbli bundna till varandra i olika exciterade tillstånd, och även de som är fria kan träffa på motsatta laddningar under vägen till kontakterna och rekombinera. Centralt i mitt arbete har varit att identifiera olika typer av exciterade tillstånd i dessa solcellsmaterial, samt att bestämma deras livstider och rekombination. Metoden för detta har varit s.k. fotoinducerad absorption, som mäter fotoexcitationernas absorptioner i infraröda våglängdsområdet. De två viktigaste resultaten som presenteras i avhandlingen är en ratekvationsmodell för fotoexcitationsdynamiken i APFO3 på ultrasnabba tidsskalor (femtosekund - microsekund) och bildandet av en rekombinationshämmande dipol vid gränsytan för P3HT och PCBM som följd av värmebehandling. Dessa resultat bidrar till förståelsen av de fotofysikaliska processerna i relaterade material.Aurinkokennoja pidetään usein ympäristöystävällisenä vaihtoehtona sähköntuotantoa varten. Suurin este niiden yleistymiselle on piipohjaisten kennojen korkea hinta. Sähköä johtavien ja puolijohtavien orgaanisten (hiilipohjaisten) yhdisteiden löytymisen myötä orgaaninen elektroniikka on tieteenalana ollut vahvassa kasvussa. Orgaanisen elektroniikan suurin vahvuus on käytettyjen materiaalien liukenevuus, ja liuosten yhteensopivuus painotekniikoiden kanssa. Orgaanisia komponentteja voi täten valmistaa painamalla, mikä lupaa merkittävästi matalampia hintoja orgaanisille aurinkokennoille. Orgaanisen elektroniikan haittapuolena on käytettyjen materiaalien epäjärjestys ja monimutkainen rakenne. Tämä heijastuu myös materiaalien valofysikaalisiin ominaisuuksiin. Väitöskirjassani olen tutkinut kahden aurinkokennoissa käytetyn polymeerin, APFO3:n ja P3HT:n valofysiikkaa. Yhdessä elektronin vastaanottajana toimivan fullereenijohdannaisen (PCBM) kanssa nämä materiaalit tuottavat tehokkasti elektroneja ja aukkoja (=positiivisia varauksia) valaistuna. Kaikki syntyneet varaukset eivät kuitenkaan osallistu aurinkokennon virran tuotantoon. Osa varauksista sitoutuvat toisiinsa muodostaen erilaisia ulkoisesti neutraaleja viritystiloja, ja osa vapaista varauksista törmäävät vastakkaisiin varauksiin matkalla kontakteille ja rekombinoivat (yhtyvät). Keskeistä työssäni on ollut viritystilojen tunnistaminen edellä mainituissa aurinkokennomateriaaleissa, sekä viritystilojen ja varausten elinaikojen ja rekombinaation selvittäminen. Työkaluna olen käyttänyt valoindusoitua absorptiota, joka mittaa viritystilojen absorptiota infrapuna-aallonpituuksilla. Tärkeimmät tulokseni ovat viritystilojen dynamiikan mallintaminen APFO3:ssa ultranopealla aikaskaalalla (femtosekunti - mikrosekunti), sekä havainto rekombinaatiota ehkäisevien dipolien muodostumisesta P3HT:n ja PCBM:n rajapinnalle lämpökäsittelyn seurauksena. Nämä tulokset lisäävät ymmärrystä vastaavien materiaalien valofysiikasta

Roll-to-Roll Fabrication of Bulk Heterojunction plastic solar cells using the reverse gravure coating technique

AbstractThe roll-to-roll reverse gravure (RG) coating technique was used to produce thin homogeneous films (∼100 nm) for organic bulk heterojunction solar cells. The conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and the active layer regioregular poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) were successfully subsequently RG coated on an ITO covered plastic substrate in ambient air. Working solar cells were achieved after annealing and thermal evaporation of the top contact. The AM1.5 power conversion efficiency (PCE) of the RG coated organic solar cells was determined to 0.74% (at 100 mW/cm2). This was very similar to the results of a reference device that was spin coated on a glass substrate in a nitrogen glove box.</jats:p

Spontaneous Charge Transfer and Dipole Formation at the Interface Between P3HT and PCBM

In the pursuit of developing new materials for more effi cient bulk-heterojunction solar cells, the blend poly (3-hexylthiophene):[6,6]-phenyl- C 61 -butyric acid methyl ester (P3HT:PCBM) serves as an important model system. The success of the P3HT:PCBM blend comes from effi cient charge generation and transport with low recombination. There is not, however, a good microscopic picture of what causes these, hindering the development of new material systems. In this report UV photoelectron spectroscopy measurements on both regiorandom- (rra) and regioregular- (rr) P3HT are presented, and the results are interpreted using the Integer Charge Transfer model. The results suggest that spontaneous charge transfer from P3HT to PCBM occurs after heat treatment of P3HT:PCBM blends. The resulting formation of an interfacial dipole creates an extra barrier at the interface explaining the reduced (non-)geminate recombination with increased charge generation in heat treated rr-P3HT:PCBM blends. Extensive photoinduced absorption measurements using both above- and below-bandgap excitation light are presented, in good agreement with the suggested dipole formation