Shockley and Queisser

Hanna and Nozik (2006) have used the detailed balance model to calculate the power conversion efficiency of single-gap and two-gap tandem solar conversion devices which employ QD absorbers capable of MEG after photon absorption. The detailed balance model has been used previously (Shockley and Queisser, 1961 Werner et al, 1994 Spirkl and Ries, 1995 Brendel et al, 1996 Wiirfel, 1997 de Vos and Desoete, 1998 Landsberg and Badescu, 2002) to calculate the limiting efficiency of ideal solar... 

Fig. 1.2 Theoretical maximum solar-to-hydrogen (STH) conversion efficiency (left axis) and photocurrent (right axis) as a function of material band gap. The theoretical maximum STH plotted here only considers the first thermodynamic principle of energy conservation and is analogous to the ultimate efficiency for a p-n junction solar cell described by Shockley and Queisser [14]...

This process describes the scattering of free carriers by the screened Coulomb potential of charged impurities (dopants) or defects theoretically treated already in 1946 by Conwell [74,75], later by Shockley [10] and Brooks and Herring [76,77]. In 1969, Fistul gave an overview on heavily-doped semiconductors [78]. A comprehensive review of the different theories and a comparison to the experimental data of elemental and compound semiconductors was performed by Chattopadhyay and Queisser in 1980 [79]. For nondegenerate semiconductors the ionized impurity mobility is given by [79] ... 

W. Shockley and H. J. Queisser, Detailed balance limit of efficiency of p-n junction solar cells, J. Appl. Phys. 32 (1961) 510-519. 

At present the IV-VI series of semiconducting materials comprises a number of the most promising materials for IR applications [1-4]. An interest in these materials is primarily because they are narrow band gap semiconductors and therefore have the potential to be employed in devices as optically active components in the near-infrared (NIR) and infrared (IR) spectral region and are hence beneficial to applications for solar cells, detectors, telecommunications relays, etc. The interest in the IV-VI materials has also grown in recent years because of the observation that they are thought to demonstrate efficient multiple exciton generation (MEG) [3,5-7]. This has implications for the efficiencies of solar cells and other applications based on these materials, especially as it provides a means by which the Shockley/Queisser efficiency limit may be overcome. 

It is this new generation of solar photon conversion devices that are covered in this book. They are less highly developed than those described in Volumes 1 and 2 of this series, bnt their promise is at least as great. That promise is two-fold on the one hand highly efficient devices with sophisticated architectures in which the Shockley-Queisser limit on efficiency is finally overcome, and on the other very low-cost plastic or organic-based devices that are cheap enough to be disposable. 

The maximal theoretical efficiency of solar energy conversion (for normal intensity of solar radiation) in silicon solar batteries with one p-n-junction is about 30% (Shockley-Queisser limit, described in 1961). For multijunction tandem solar batteries and for batteries with an optical light condenser the theoretical limit is higher. The practical efficiency is lower and depends on several factors, including the crystalline modification of silicon and the thickness of the semiconductor, where photons are adsorbed. For high thickness silicon batteries the efficiency reaches about 20%. For low thickness batteries made from amorphous silicon it is 5-10%. The maximum practical conversion efficiency silicon has is at a temperature of about 25 C. With rising temperatures the efficiency diminishes. The battery is often covered by a thin layer of silicium nitride that reflects UV light and prevents a temperature rise (antireflection layer). 

The nontraditional approaches in photoelectrochemistry encompass systems and effects where the conversion efficiency exceeds that of the single junction Shockley-Queisser limit (defect level absorbers, multiple exciton generation, singlet fission). In a second approach, the use of hot electrons for initiating electrochemical reactions which otherwise would necessitate large overvoltages is attempted. Besides the direct use of non-thermalized hot electrons from the absorber surface [107], recently, contributions from the decay of surface plasmons have been investigated, too [108, 109]. The third approach is based on... 

Semiconductor NCs have been incorporated into solar cells in different configurations, for example (a) photoelectrodes composed of quantum dot arrays, (b) metal-semiconductor photovoltaic cells,(c) NC-polymer solar cells and (d) quantum dot sensitized solar cells. This field has been the focus of intense research in recent years because of the possibility that quantum dot-based solar cells can overcome the Shockley-Queisser photoconversion limit. This possibility relies on two feasible processes hot carrier extraction and multiple exciton generation (MEG). 

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