Thin‐film silicon solar cell technology

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Abstract
This paper describes the use, withinp–i–n‐ andn–i–p‐type solar cells, of hydrogenated amorphous silicon (a‐Si:H) and hydrogenated microcrystalline silicon (μc‐Si:H) thin films (layers), both deposited at low temperatures (200°C) by plasma‐assisted chemical vapour deposition (PECVD), from a mixture of silane and hydrogen. Optical and electrical properties of thei‐layers are described. These properties are linked to the microstructure and hence to thei‐layer deposition rate, that in turn, affects throughput in production. The importance of contact and reflection layers in achieving low electrical and optical losses is explained, particularly for the superstrate case. Especially the required properties for the transparent conductive oxide (TCO) need to be well balanced in order to provide, at the same time, for high electrical conductivity (preferably by high electron mobility), low optical absorption and surface texture (for low optical losses and pronounced light trapping). Single‐junction amorphous and microcrystallinep–i–n‐type solar cells, as fabricated so far, are compared in their key parameters (Jsc, FF,Voc) with the [theoretical] limiting values. Tandem and multijunction cells are introduced; the μc‐Si: H/a‐Si: H or [micromorph] tandem solar cell concept is explained in detail, and recent results obtained here are listed and commented. Factors governing the mass‐production of thin‐film silicon modules are determined both by inherent technical reasons, described in detail, and by economic considerations. The cumulative effect of these factors results in distinct efficiency reductions from values of record laboratory cells to statistical averages of production modules. Finally, applications of thin‐film silicon PV modules, especially in building‐integrated PV (BIPV) are shown. In this context, the energy yields of thin‐film silicon modules emerge as a valuable gauge for module performance, and compare very favourably with those of other PV technologies. Copyright © 2004 John Wiley & Sons, Ltd.