Inorganic Thin Film Solar Cells Research Articles

Degradation of organic photovoltaic devices: a review

Organic solar cells are considered as low-cost photovoltaic technology driven by potentially reduced cost production via high throughput processes, such as printing and lower cost of starting materials. However, commercial realization of this technology is hindered by poor device lifetimes due to environmental degradation of the devices. Under standard test conditions, these devices show lifetimes much shorter in comparison with conventional silicon or other inorganic thin-film solar cells. The lifetimes of organic solar cells are strongly dependent on device processing, measurement (temperature, humidity and light intensity) and encapsulation conditions in addition to intrinsic nature of the constituent materials and their reactivity with each other. Recently, there has been a conscious effort to improve the lifetimes of organic solar cells and strategies such as incorporation of oxide buffer layers, change in the device architecture to inverted geometry and improved materials have been demonstrated to result in improved device lifetimes. In this manuscript, the authors present a review of the degradation in organic solar cells and associated mechanisms, approaches undertaken to improve the device reliability characteristics and lifetimes, the methods to study degradation and finally a brief discussion on encapsulation of the devices.

Analysis of voltage and temperature dependent photocurrent collection in p3ht/pcbm solar cells

Current-voltage (J-V) analysis of poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend organic solar cells (OSC) at various temperatures has been recorded and analyzed. The photovoltaic parameters extracted from a lumped circuit analysis completely describe the illuminated J-V data from far reverse bias to beyond the open circuit voltage (Voc). A simple model for carrier collection, previously applied to inorganic thin film solar cells, has been used to describe the voltage dependence of the photocurrent, JL(V), with only one adjustable parameter, Lc/D, the ratio of the carrier collection length to the active-layer thickness. Measured J-V curves of a variety of OSCs with varying thickness and blend ratios are closely fit with this model. Effect of resistive and collection losses has been quantified and removed, allowing the intrinsic junction behavior to be uncovered. The temperature dependence of Voc is linear with negative temperature coefficient, dVoc/dT,∼ −1 mV/K. The values of the effective bandgap of the blend obtained from the intercept at T = 0 K decrease with the increase of the PCBM concentration. Our data support the idea of existence of mid-bandgap states, which increase with the increase in the disorder in the active layer.

Efficiency Inorganic Thin Film Solar Cells with Flexible Substrate

The development of CdTe/CdS solar cells on flexible substrates is reviewed in this article. Photovoltaic structures on lightweight and flexible substrates have several advantages over the heavy glass based structures in both terrestrial and space applications. The cells mounted on flexible foil are not fragile, the requirements of the supporting structures are minimum and they can be wrapped onto any suitably oriented or curved structures. The specific power of the solar cells is an important factor in space applications and hence development of photovoltaic devices on light weight substrates is interesting. CdTe is one of the leading candidates for photovoltaic applications due to its optimum band gap for the efficient photo-conversion and robustness for industrial production with a variety of film preparation methods. Flexible solar cells with conversion efficiencies exceeding 11% have been developed on polyimide foils. The development of CdTe devices on metallic substrates is impeded due to the lack of a proper ohmic contact between CdTe and the substrate. The polymer substrate has the advantage that the devices can be prepared in both “superstrate” and “substrate” configurations.