Structure formation and evolution in semiconductor films for perovskite and organic photovoltaics

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Structure formation and evolution in semiconductor films for perovskite and organic photovoltaics Andrew J. Pearsona) Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, U.K. (Received 20 December 2016; accepted 21 February 2017)

The research and development of novel photovoltaic technologies is going through a golden era, thanks to the demonstration of remarkable efficiencies across a broad range of semiconductor classes and device architectures. In parallel with these developments, the opportunities for characterizing the structure of a semiconductor film in situ of a processing step have also increased, to the extent that in situ and in operando experiments are becoming readily accessible to researchers. These combined advances represent the subject matter of this article, wherein studies that improve our understanding of structure formation and evolution in perovskite and organic semiconductor films for innovative solar cells are reviewed. Although focus is placed on the dynamics of semiconductor film formation, the review also highlights recent research on environmental testing, a key component in the development of materials with high intrinsic stability.

I. INTRODUCTION

Photovoltaics (PVs) have evolved over the past several decades to become a truly global renewable technology.1–3 Since 1995 the annual growth rate of deployed solar power capacity has averaged 43% and as of writing over 230 GWp of installed capacity exists worldwide.4,5 To build upon this trend, and benefit further from largescale PV deployment, continued investment, research and development is required such that newer materials and manufacturing processes can be commercialized.6 As with many technologies, the goal for PV is to realize systems that offer high performance at intrinsically low cost. Importantly, the solar cells and solar modules of the future will be developed not only for traditional forms of power generation, such as farms and rooftop installations, but also for a wider range of innovative applications than is currently realized. Specifically, examples where direct PV module incorporation is desired include building integrated PV, portable PV, and PV interfaced with flexible electronics. Recent breakthroughs have brought these opportunities much closer to reality, and as a consequence contemporary PVs R&D describes a vibrant and highly dynamic activity. The purpose of this review is to highlight recent advances in one area of PV research, namely, the knowledge gained through in situ measurements that

Contributing Editor: Dean DeLongchamp a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.87

relate the optoelectronic properties of a device to the composition and crystal structure of the semiconductor layer.7 Structure–property relationships often provide the basis for realizing improvements in technology performance as they allow researchers to relate physical processes to key lengthscales within a material or to construct a framework for the targeted design of improved mater