If a photovoltaic (PV) technology is assessed today in a technical framework, then efficiency is the most commonly addressed parameter, followed by service lifetime. Cost, as the third parameter of the "magic triangle", is even less often reported. However, if a new technology is prepared to enter a market, other important parameters have to be considered, especially if non-standard PV applications are targeted.

Organic photovoltaic (OPV) is a well known but young PV technology of the so called third generation, which offers unique advantages for integrated products such as building integrated photovoltaics (BIPV). In this contribution we would like to highlight some of the advantages and challenges which are specific to the application of OPV in the field of building integration. Architectural design features of OPV include the ability to adapt semi-transparency, color and shape of the module. Moreover, glass-laminated OPV modules are deemed suitable for BIPV because of their ease of integration, good fire resistance, high energy harvest per nominal watt-peak and long lifetimes.

We investigate the built-in voltage in organic bulk heterojunction solar cells using electroabsorption spectroscopy based on the Stark effect, i.e. the variation of the absorption energies of a material caused by an electric field. Due to spectral contributions of permanent dipoles, a novel approach for evaluating the EA spectra is required. We use a fitting routine analyzing a broad spectral range instead of using only a single wavelength. A reliable quantitative determination of the built-in voltage is achieved.

Light-induced electron spin resonance (LESR) study of polymer solar cells has been performed to investigate accumulated hole carriers in these devices under device operation. We analyzed clear correlation between the number of accumulated holes in regioregular poly(3-hexylthiophene) (P3HT) evaluated by LESR and the deterioration of device performance (Voc, Jsc) observed using the same device under simulated solar irradiation. The effects of hole accumulation with deep trapping levels formed in P3HT at the organic interfaces on the performance are examined by considering interfacial electric dipole layers and charge-carrier scattering by accumulated holes.

Morphology of the active layer in bulk heterojunction P3HT:PCBM organic solar cell was studied using Monte Carlo (MC) and coarse-grained dynamics simulations. While coarse-grained molecular dynamics allow us to quickly estimate the P3HT:PCBM interfacial energy of bilayer structure as a function of underlying layer thickness, bridging the dimension and time gap between dynamics simulations and experiment is computationally expensive and therefore not viable. Using MC technique with input from dynamics simulations allowed us to speed up the calculation and obtain final morphological information based on energetics and entropy, and at the same time retained the physics fidelity in-built in our validated coarse-grained model. The final structure gives phase separated domains with dimension of approximately 12 nm, on par with reported experimental result. The method can be applied to other organic photovoltaics systems to predict active layer morphology relevant for device performance or 3-dimensional device modelling at continuum level.