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One of the advantages of Cu(In,Ga)(S,Se)2 (CIGSSe) thin film solar cells is the lower temperature sensitivity of the solar cell parameters as compared to conventional silicon-based technologies. To further improve and to tailor CIGSSe temperature behavior for different environments, it is important to gain a detailed understanding of the microscopic mechanisms involved. The goal of the current study is to elucidate the impact of the individual functional layers within the CIGSSe solar cell stack on the temperature dependence of the overall cell performance. For this purpose, temperature-dependent current-voltage measurements were performed on a selected set of CIGSSe cells, containing a systematic variation of functional layers. The experimental results demonstrate that the absorber layer exhibits the largest influence on the temperature dependence of the power efficiency. An analysis of the contributing parameters revealed that the temperature-dependence of the power efficiency is mainly governed by a change in the open-circuit voltage. The temperature coefficient of the open-circuit voltage is analyzed in terms of the cell's physical parameters, including their minimum band gap and the temperature-dependence of the dark saturation current.

We use a calibrated realistic 2D device simulation structure of a single cell from a monolithic interconnected Cu(In,Ga)(Se,S) 2 solar module to investigate the impact of modifications of the patterning laser scribe P1 and the trench properties on the energy yield. This particularly includes examining the change of the low light behaviour and the performance ratio (PR). In order to study the effects of the P1 characteristics, we performed a variation of the P1 width, the absorber doping concentration within the P1 trench as well as a variation of the Mo(Se,S) 2 band gap and the doping concentration. We simulated temperature-dependent current-voltage characteristics for different irradiances and apply the weather data of three different locations to calculate the PRs. An increased P1 width and decreased absorber doping concentration was found to increase the P1 (parallel) shunt resistance due to a reduced horizontal hole current component between the separated back electrodes. A higher shunt resistance enhances the low light behaviour of the solar cell and consequently leads to an improvement of the PR. A decreased Mo(Se,S) 2 band gap and doping concentration increases the valence band barrier at the Cu(In,Ga)(Se,S) 2 /Mo(Se,S) 2 interface and we obtained a moderate P1 shunt improvement accompanied by a strong PR enhancement. The increased barrier height enhanced the low light and temperature behaviour of the fill factor finally leading to the PR enhancement.

The modeling of Cu(In,Ga)(Se,S) 2 thin film solar cells enables us to understand device behavior while a reliable simulation with forecasting purpose needs to cover manifold measurement responses. We built up a simulation model to reproduce thermal admittance spectra, capacitance–voltage profiles, quantum efficiency and current–voltage ( I–V ) measurements in a broad temperature range from 130 K to 330 K with one parameter set. The comprehensive optical and electrical simulation model has been created as baseline for an indium sulfide buffered Cu(In,Ga)(Se,S) 2 solar cell based on measurement outcome and material characterization. The model ascribes the observed N1 feature ascribing it to a valence band barrier between Cu(In,Ga)(Se,S) 2 and Mo(Se,S) 2 back contact which is also responsible for the roll-over behavior in I–V measurements. A highly doped p + layer near the heterointerface is accountable for superposition failure of dark and light I–V curves and kink shape at low temperatures. Two-dimensional simulations further show roll-over dependence on back contact inhomogeneities due to sulfur fluctuations.

Charge separation is an important elementary step in solar cells with donor/acceptor heterojunctions. In this work, light-induced electron spin resonance (LESR) is used to study the charge transfer and recombination of photo-generated charge carriers in inorganic/organic hybrid composites of CuInS2 nanoparticles with the conjugated polymer poly(3-hexylthiophene) (P3HT) or the electron acceptor phenyl-C61-butyric acid methyl ester (PCBM), respectively. After synthesis, the CuInS2 nanoparticles are surrounded by a ligand shell composed of relatively long-chained organic molecules. A ligand shell modification with hexanethiol was applied to the CuInS2 nanoparticles to study the influence of the ligand shell on the charge separation process. The effect of the hexanethiol treatment on the initial ligand shell present after synthesis was analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). We demonstrate that charge transfer in both the CuInS2/P3HT and CuInS2/PCBM composites is possible and in case of P3HT strongly influenced by the ligand shell. The recombination kinetics of photo-generated charge carriers reveals that trapping is especially governed by the organic semiconductor. Laboratory solar cells with CuInS2/P3HT or CuInS2/PCBM as the photoactive layer are presented as well.

We use solvent additives as a simple method to tune the photovoltaic performance of poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojuncton solar cells. 1,2-dichlorobenzene (oDCB) was used as the reference solvent; chlorobenzene (CB) and 1,2,3,4-tetrahydronaphthalene (THN) were used as additives to influence film formation. An increase in the short circuit current and the power conversion efficiency of solar cells with blends cast from mixed solvents was observed. Blends prepared with THN, the highest boiling point solvent, resulted in the best device performance, while blends prepared with the pure reference solvent resulted in the lowest photocurrent. In-plane investigations of the morphology using transmission electron microscopy (TEM) revealed improved phase segregation for blends prepared with mixed solvents, and increased crystallinity in the P3HT phase is demonstrated using atomic force microscopy (AFM) coupled with Kelvin probe force microscopy (KPFM). Optical modeling reveals that the increase in the photocurrent is not due to changes in the optical properties of the blends. Electrical characterization reveals that the electron mobilities decrease slightly in blends cast from mixed solvents, corresponding to a decrease in the fill factor and an increase in P3HT crystallinity observed at the surface of the blend. The increase in the photovoltaic performance is discussed in terms of increased charge separation at the donor–acceptor interface due to increased ordering in the P3HT phase induced by the solvent additives.

We report on field effect mobility measurements in methanofullerene [6,6]-phenyl C61C61-butyric acid methyl ester (PCBM) films and in blends of poly(3-hexylthiophene) (P3HT) and PCBM, identical to those used in polymer solar cells. Electron mobilities in the order of 10-3cm2/Vs were found in the pure PCBM films, and electron mobilities of 10-4cm2/Vs were found in P3HT:PCBM blends at room temperature. Mobility measurements on the blends yielded electron mobilities of a factor 10 lower than those in the pure films. Temperature dependent measurements were performed to investigate the temperature dependence of the mobility in both films. In order to understand the discrepancy in the electron mobility between pure film and blend, we investigated the parasitic effects of the contacts on the measured value of mobility, but found that losses in the bulk dominate the current.