**Abstract**

The III-V compound solar cells represented by GaAs solar cells have contributed as space and concentrator solar cells and are important as sub-cells for multijunction solar cells. This chapter reviews progress in III-V compound singlejunction solar cells such as GaAs, InP, AlGaAs and InGaP cells. Especially, GaAs solar cells have shown 29.1% under 1-sun, highest ever reported for single-junction solar cells. In addition, analytical results for non-radiative recombination and resistance losses in III-V compound solar cells are shown by considering fundamentals for major losses in III-V compound materials and solar cells. Because the limiting efficiency of single-junction solar cells is 30-32%, multi-junction junction solar cells have been developed and InGaP/GaAs based 3-junction solar cells are widely used in space. Recently, highest efficiencies of 39.1% under 1-sun and 47.2% under concentration have been demonstrated with 6-junction solar cells. This chapter also reviews progress in III-V compound multi-junction solar cells and key issues for realizing high-efficiency multi-junction cells.

**Keywords:** solar cells, GaAs, InP, InGaP, III-V compounds, multi-junction, tandem, high efficiency, radiation-resistance

## **1. Introduction**

The III-V compound solar cells represented by GaAs solar cells have advantages such as high-efficiency potential, possibility of thin-films, good temperature coefficient, radiation-resistance and potential of multi-junction application compared crystalline Si solar cells. The III-V compound solar cells have contributed as space and concentrator solar cells and are important as sub-cells for multi-junction solar cells. As a result of research and development, high-efficiencies [1, 2] have been demonstrated with III-V compound single-junction solar cells: 29.1% for GaAs, 24.2% for InP, 16.6% for AlGaAs, and 22% for InGaP solar cells. **Figure 1** shows historical record-efficiency of GaAs, InP, AlGaAs and InGaP single-junction solar cells along with their extrapolations [3].

The data can be fitted with the Goetzberger function [4]:

$$\boldsymbol{\eta}(\mathbf{t}) = \eta\_{\text{limit}} [\mathbf{1} - \exp \left. \mathbf{(t}\_0 - \mathbf{t}) / \mathbf{c} \right|, \tag{1}$$

where η(t) is the time-dependent efficiency, ηlimit is the practical limiting efficiency, t0 is the year for which η(t) is zero, t is the calendar year, and c is a characteristic development time. Fitting of the curve was done with three parameters which are given in **Table 1**. The extrapolations show that the progress of

#### **Figure 1.**

*World record efficiencies of GaAs, InP, AlGaAs and InGaP single-junction solar cells over years. Solid and dashed lines are the fitted trajectories using Eq. (1).*


**Table 1.**

*Fitting parameters for various solar cells.*

**Figure 2.** *Calculated and obtained efficiencies of single-junction single-crystalline and polycrystalline solar cells.*

## *High-Efficiency GaAs-Based Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.94365*

efficiencies is converging or will converge soon, which is mainly bounded by the Shockley-Queisser limit [5].

**Figure 2** shows calculated and obtained efficiencies of single-junction singlecrystalline and polycrystalline solar cells [6]. Because the limiting efficiency of single-junction solar cells is 30-32% as shown in **Figure 2**, multi-junction solar cells have been developed and InGaP/GaAs based 3-junction solar cells are widely used in space. Recently, highest efficiencies of 39.2% under 1-sun and 47.1% under concentration have been demonstrated with 6-junction solar cells [7].

This Chapter reviews progress in III-V compound single-junction solar cells such as GaAs, InP, AlGaAs and InGaP cells. In addition, analytical results for nonradiative recombination and resistance losses in III-V compound solar cells by considering fundamentals for major losses in III-V compound materials and solar cells. This chapter also reviews progress in III-V compound multi-junction solar cells and key issues for realizing high-efficiency multi-junction cells.
