Numerical Analysis of Photoenhanced Electric Currents in Molecular Materials

This paper presents numerical calculations of photoenhanced current-applied voltage and photoenhanced current-light intensity characteristics with regard to the exciton diffusion length, lifetime of excitons and rate of exciton surface quenching. Dependencies of this type cannot be obtained analytically. It is shown that the increase in diffusion length causes the decrease in current in the case of strong surface quenching of excitons. Simultaneously, it is shown that the quality of crystals influences the photoenhanced current. A better quality of crystals causes the increase in the current in the case of weak surface quenching of excitons

Electric Current Flow through Tetracene Layer-Anthracene Crystal Junction

Theoretical and experimental analysis was carried out on electric currents limited by the potential barrier governing the flow of holes from the tetracene layer to the anthracene crystal. Theoretical spatial distributions of charge carriers near the barrier were determined, as well as current-field dependences for the currents flowing through the investigated junction in the presence and in the absence of illumination. A current-field characteristic of the junction conditioned current is described by dependence of the j ∝ E$\text{}_{0}^{3}$ type in the presence of illumination and by the j ∝ E$\text{}_{0}^{2l+1}$ type in the lack of illumination, where l is the characteristic parameter of the trap distribution. Experimental research of the hole currents flowing through the polycrystalline tetracene layer-anthracene monocrystal junction confirmed the theoretical predictions about the current-field characteristics. A remarkably unequivocal confirmation was obtained for the current-field dependences in the presence of illumination

Photovoltaic Devices Based on Planar II-VI Semiconductor / Molecular Semiconductor Heterojunction

Artykuł przedstawia wybrane wyniki badań własnych nad układami hybrydowymi zbudowanymi na bazie złącza półprzewodnik nieorganiczny II-VI / półprzewodnik organiczny. Na podstawie analizy położenia pasm energetycznych warstw wchodzących w skład wytworzonych ogniw oraz charakterystyk spektralnych prądu zwarcia tych urządzeń, określone zostały procesy prowadzące do fotogeneracji nośników ładunku w badanych układach. W ogniwach zbudowanych na bazie złącz CdS/ZnPc oraz ZnTe/F16ZnPc zaobserwowano zarówno generację bezpośrednią w półprzewodniku nieorganicznym (przejście pasmo-pasmo), jak i generację wynikającą z dysocjacji ekscytonów wzbudzonych w półprzewodniku molekularnym, zachodzącą na złączu obydwu półprzewodników. W przypadku układów zbudowanych na bazie złącza CdTe/DIP, zaobserwowano jedynie fotogenerację drugiego typu.This article presents chosen results of research on hybrid solar cells based on inorganic II-VI semiconductor/molecular semiconductor heterojunctions. On the basis of energetic structure of fabricated devices and short-circuit current spectral response measured for these cells possible processes leading to photogeneration of free charge carriers were determined. For the cells based on CdS/ZnPc and ZnTe/F16ZnPc heterojunctions two processes were identified: direct photogeneretaion in inorganic semiconductors via band-to-band transitions and dissociation of excitons generated in molecular semiconductors that takes place at the interface of both semiconductors forming the junction. In contrast, only the latter process was observed in case of devices with CdTe/DIP heterojunction

Charge Carrier Generation Caused by X-Rays in Organometallic Materials

Organometallic compounds play an exceptional role among organic compounds. Due to their structure a number of these compounds demonstrate interesting properties in various phenomena. Organometallic compounds show special properties in the case of X-ray absorption owing to considerable differences between the absorption coefficients of metals and light elements. The analysis of processes of charge carrier generation as a result of X-ray absorption in chosen organometallic compounds is the subject of this paper. Spectral dependences of charge carrier photogeneration efficiency around the Cu K-edge in copper phthalocyanine and copper acetylacetoniane have been specially considered. It has been observed that the photocurrent spectrum in these materials follows the absorption spectrum but mutual relation is not directly proportional. Experimental results connected with current-voltage and current-intensity characteristics have been analysed, as well. The obtained relationships have been compared with adequate results connected with charge carrier photogeneration in visible area and UV in organic materials. It has been observed that the X-ray photogeneration of charge carriers in the examined range of energy differs from the mechanisms of charge carrier generation in visible area and UV. The basic differences arise from the participation of secondary electrons, which are generated due to Auger electrons, Compton effect, and metal fluorescence. The process of charge carrier generation as a result of X-rays absorption is characterized by strong recombination of charge carriers in channels in which charge carriers are generated by high energetic secondary electrons

Single and Double-Layer Organic Solar Cells

Omówiona została zasada działania organicznych ogniw fotowoltaicznych na przykładzie ogniw jedno- i dwuwarstwowych. Przedstawione zostały procesy prowadzące do fotogeneracji swobodnych nośników ładunku w układach organicznych, ze szczególnym uwzględnieniem procesu dyfuzji oraz dysocjacji ekscytonu na złączu dwóch materiałów. Przytoczone zostały podstawowe wyrażenia na wartość napięcia fotowoltaicznego dla układów jedno- i dwuwarstwowych oraz wybrane wyniki badań własnych dla ogniw dwuwarstwowych.This article explains operational principles of organic solar cells for one-layer and bilayer planar devices. A short description of processes leading to photogeneration of free charge carriers, with special emphasis on exciton diffusion to a junction of two materials followed by exciton dissociation at this junction is given. Basic equations for photovoltage obtained for one- and bilayer devices are presented. Moreover, chosen results of research run by our group for bilayer planar solar cells are shown