Theoretical analysis and numerical simulations identify the detailed balance performance limits

A basic schematic, and band-diagram of perovskite solar cells. ETL stands for Electron Transport Layer and HTL stands for Hole Transport Layer

Perovskite based solar cells use a material called perovskite to harvest energy from sunlight, hence the name. It is the fastest-growing technology in terms of reported efficiency in the history of photovoltaics. For this reason, perovskite based solar cells generated tremendous interest among the photovoltaic research community globally. But even after few years of persistent research and publication, practical limits of this material-system is not clear. Prof. Nair’s group in IITBNF have done detailed calculations using coupled optical and electrical charge carrier transport simulations to find out the practical limit of efficiency and fill-factor of these devices.

Perovskite based solar cells became suddenly popular among global photovoltaic community because of its meteoric improvement in reported efficiencies in the last half of this decade. The fact that most of the aspects of this material-device platform are not optimized yet is giving us hope of finding a true alternative to current crystalline silicon solar cells whose efficiency and cost effectiveness have almost reached near saturation for a while. The name perovskite refers to the crystal structure of a mineral named after Russian mineralogist Lev Perovski. It can be made with a number of material combinations (typically halides like methyl ammonium lead trihalide). In perovskite based solar cells this material is used in between electron and hole transport layers to harvest light into charge carriers (figure). The charge carriers generated are effectively transported to the electron and hole transport layers because of the large diffusion length of charge carriers with large extinction coefficient in the material.

In this work, the authors have identified the limits of theoretical performance of this device family in the presence of radiative and Auger recombination. The group’s detailed numerical simulations also identified the factors responsible for sub-optimal performance of the perovskite based solar cells reported so far. Finally, the authors have provided a comprehensive modelling framework to improve the performance of these solar cells and obtained a calculated efficiency of 29.1% for the scheme they’ve developed, which is just 0.4% lower than the theoretical limit.

- Sanchar Acharya

Work funded/ supported by: Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy and the Government of India’s Department of Science and Technology

Published paper: Sumanshu Agarwal and Pradeep R. Nair, “Device engineering of perovskite solar cells to achieve near ideal efficiency”, Applied Physics Letters, Vol. 107, pp. 123901(2015).SSSSSS