Photovoltaics early applications

Use of solar panels or photovoltaics (PVs) is another popular way to generate solar electricity. The space program is perhaps the most recognized user of PVs and is responsible for most of the advancements in PVs. Many people are familiar with PVs through small applications such as calculators and perhaps solar water heaters, but early forays in PV experimentation were little more than noted side observations in non-PV experiments. 

Despite the extensive application of ruthenium complexes in DSSC, transition metal containing polymers have received relatively little attention in the fabrication of polymeric photovoltaic cells. Most of the early works on ruthenium containing polymers were focused on the light-emitting properties.58-60 Several examples of ruthenium terpyridine/bipyridine containing conjugated polymers and their photoconducting/electroluminescent properties were reported.61,62... 

Applications of undoped (semiconducting) CPs fill only one line in Table 2. None has reached the market yet, and as for other classes of CPs, several applications that were advocated in the past have failed to meet the necessary requirements. In the early 1980s, for instance, a significant amount of work was invested in the study of CP photovoltaic cells [130], but the subject is no longer active. 

Early studies of metal-CP interfaces, particularly Schottky barrier metal-CP diodes, were motivated primarily by possible applications in photovoltaic energy conversion. Work on trans-PA as of 1985 was reviewed by Kanicki [232]. Unfortunately, the photovoltaic yield of CPs never exceeded about 1%, so interest in that field subsided, and it will not be considered further here. A more recent review is given in Ref. 233. 

Photovoltaic solar power conversion was the first major application proposed for a-Si H and to date is the largest in production. The first devices were reported by Carlson and Wronski in 1976 and had an efficiency of only 2-3%. Some of the early devices were Schottky barrier cells, but were quickly discarded in favour of p-i-n cells. Since the first report, there has been a remarkable increase in the efficiency of the cells, increasing by roughly 1 % conversion efficiency per year, to a present value of 14%, as is shown in Fig. 10.17. The increase has resulted from a variety of innovations in the design, materials, and structure of the cells. The electronic properties of the solar cell are described next and then these innovations are outlined more or less in the order in which they occurred. 

LeComber (1975) showed that by suitable doping, a-Si could be made n- or p-type. These properties, in conjunction with the fact that plasma-deposition processes are generally amendable to large areas, were such that much of the early interest in a-Si was directed to photovoltaic applications (Carlson and Wronski, 1976 Kuwano. 1986). It was quickly recognized, however, that the requirements for photovoltaic applications were, in many respects, similar to those for xerographic photoreceptors. 

The photovoltaic effect in conjugated polymers and its application to solar cells was investigated in the late 1970s and early 1980s (Kanicki, 1986). Cells fabricated with PAc had relatively short lifetimes which resulted in the proposal that they could perhaps be commercialised as disposable power sources. The development of commercial solar cells has, however, been slow and now lags behind that of LEDs, despite the much more recent discovery of... 

Photovoltaic devices typically consist of a series of thin semiconductor layers that are designed to convert sunlight to direct-current electricity (see SEMICONDUCTORS). As long as the device is exposed to sunlight, a photovoltaic (PV) cell produces an electric current proportional to the amount of light it receives. The photovoltaic effect, first observed in 1839, did not see commercial application until the 1950s when photovoltaic modules were used to power early space satellites. Many good descriptions of the photovoltaic phenomenon are available (7). 

The absorption, emission, and redox properties of squaraines make them highly suited for applications as photosensitizers. In view of this, the early studies on squaraines were focused on thin photovoltaic and semiconductor photosensitization properties [1,4,5,91-97], Champ and Shattuck [98] first demonstrated that squaraines could photogenerate electron-hole (e-h) pairs in bilayer xerographic devices. Subsequently, extensive work has been carried out on the xerographic properties of squaraines [2,24,34,47,48,99,100], and these properties have been reviewed recently [11]. In an extensive smdy on the correlation s between cell performance and molecular structure in organic photovoltaic cells, squaraines were found to have much better solar energy conversion efficiencies than a variety of other merocyanine dyes [4,5]. 

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