Jens A. Hauch

Physics of organic bulk heterojunction devices for photovoltaic applications

We present investigations of organic photovoltaic devices consisting of bulk heterojunction layers made from several material combinations. All of the investigated systems reveal close similarities to the behavior of classical pn-junction devices. The consequences of the pn-junction-like behavior on the device parameters and performance are presented. Furthermore, device characteristics and parameters of the pristine materials are correlated, resulting in a model that permits an identification of high potential materials, a performance prediction, and a device optimization. The resulting model is able to predict an open circuit voltage and a fill factor and their evolution with the light intensity or thickness of the active layer. It simplifies the identification of the internal morphology and therefore the choice of appropriate solvents. Necessary parameters concerning the choice of electrode materials are also provided.

The impact of water vapor transmission rate on the lifetime of flexible polymer solar cells

In this paper we perform accelerated lifetime testing on high efficiency flexible poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) solar cells encapsulated with food package quality barrier films with a water vapor transmission rate of 0.2 g/(m2 day) at 65 °C/85% relative humidity. We show that lifetimes exceeding 1250 h, even at high temperature/high humidity conditions, may be reached, proving that organic solar cells are significantly less sensitive against the environmental effects of water and oxygen than previously expected.

Barix multilayer barrier technology for organic solar cells

The effect of multilayer barrier materials on the lifetime of organic photovoltaic cells has been investigated. For thin film encapsulated cells a protective layer was used to prevent damage during barrier layer deposition. No post deposition effects developed after dry box storage. In accelerated temperature and humidity lifetime testing the degradation of the encapsulated cells can be related to the loss of effective cell area. An extrapolation of the lifetime at room conditions has been quantitatively determined by comparing the cell degradation with the loss of Ca in a Ca-oxidation test. The results indicate a barrier permeation rate of 10-4 gr/[m2* day] for these samples, corresponding to a lifetime of greater than 5000 hours. Routes to improvement of the OPV cell lifetime are discussed.

Impact of PID on industrial rooftop PV-installations

Potential induced degradation (PID) causes severe damage and financial losses even in modern PV-installations. In Germany, approximately 19% of PV-installations suffer from PID and resulting power loss. This paper focuses on the impact of PID in real installations and how different evaluated time intervals influence the performance ratio (PR) and the determined degradation rate. The analysis focuses exemplarily on a 314 kWp PV-system in the Atlantic coastal climate. IR-imaging is used for identifying PID without operation interruption. Historic electric performance data are available from a monitoring system for several years on system level, string level as well as punctually measured module string IV- curves. The data sets are combined for understanding the PID behavior of this PV plant. The number of PID affected cells within a string varies strongly between 1 to 22% with the string position on the building complex. With increasing number of PID-affected cells the performance ratio decreases down to 60% for daily and monthly periods. Local differences in PID evolution rates are identified. An average PR-reduction of -3.65% per year is found for the PV-plant. On the string level the degradation rate varied up to 8.8% per year depending on the string position and the time period. The analysis reveals that PID generation and evolution in roof-top installations on industrial buildings with locally varying operation conditions can be fairly complex. The results yield that local operating conditions, e.g. ambient weather conditions as well as surrounding conditions on an industrial building, seem to have a dominating impact on the PID evolution rate.