Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells

Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-accepting (A) materials to split excitons into charges. However, the use of D-A blends intrinsically limits the photovoltage and introduces morphological instability. Here, we demonstrate that polycrystalline films of chemically identical molecules offer a promising alternative and show that photoexcitation of α-sexithiophene (α-6T) films results in efficient charge generation. This leads to α-6T based homojunction organic solar cells with an external quantum efficiency reaching up to 44% and an open-circuit voltage of 1.61 V. Morphological, photoemission, and modelling studies show that boundaries between α-6T crystalline domains with different orientations generate an electrostatic landscape with an interfacial energy offset of 0.4 eV, which promotes the formation of hybridised exciton/charge-transfer states at the interface, dissociating efficiently into free charges. Our findings open new avenues for organic solar cell design where material energetics are tuned through molecular electrostatic engineering and mesoscale structural control

Oral health sensations associated with illicit drug abuse

Objectives: To investigate oral health sensations (short term oral health effects) associated with illicit drug abuse. In addition, to identify variations in oral health sensations produced by different illicit drugs. Subject: Young adults in a drug rehabilitation programme in Hong Kong, China. Method: Self-completed questionnaire about their previous pattern of drug abuse and oral health sensations experienced (recalled). Results: All (119) subjects were poly-drug abusers (abused one or more illicit drugs in the past). Amphetamine-based drugs such as methamphetamine ('speed') and methylenedioxymethamphetine ('ecstasy') were commonly abused. A wide range of oral health sensations were reported on recall of their abuse of illicit drugs; most frequently dry mouth (95%, 113). Types of illicit drugs abused were associated with oral health sensations reported (P < 0.001). 'Ecstasy' abusers more frequently reported chewing (P < 0.001), grinding (P < 0.001), and TMJ tenderness (P < 0.001) compared to non-'ecstasy' abusers. Conclusion: Illicit drug abuse produces many oral health sensations. Types of drugs abused were associated with oral sensations produced, and behavioural effects that may manifest as depression, anxiety, memory loss and various neuropsychotic disorders.8,9 In some cases drug abuse can result in death by various means: malignant hyperthermia, internal bleeding, fatal overdosing and through allergic reactions.10,11 Likewise, there have been reports on the long term clinical effects of illicit drug abused on oral health, © British Dental Journal 2005.link_to_subscribed_fulltex