Title: Collection-limited theory interprets the extraordinary response of single semiconductor organic solar cells

Abstract

The bulk heterojunction (BHJ) organic photovoltaic (OPV) architecture has dominated the literature due to its ability to be implemented in devices with relatively high efficiency values. However, a simpler device architecture based on a single organic semiconductor (SS-OPV) offers several advantages: it obviates the need to control the highly system-dependent nanoscale BHJ morphology, and therefore, would allow the use of broader range of organic semiconductors. Unfortunately, the photocurrent in standard SS-OPV devices is typically very low, which generally is attributed to inefficient charge separation of the photogenerated excitons. In this paper, we show that the short-circuit current density from SS-OPV devices can be enhanced significantly (~100-fold) through the use of inverted device configurations, relative to a standard OPV device architecture. This result suggests that charge generation may not be the performance bottleneck in OPV device operation. Instead, poor charge collection, caused by defect-induced electric field screening, is most likely the primary performance bottleneck in regular-geometry SS-OPV cells. We justify this hypothesis by: (i) detailed numerical simulations, (ii) electrical characterization experiments of functional SS-OPV devices using multiple polymers as active layer materials, and (iii) impedance spectroscopy measurements. Furthermore, we show that the collection-limited photocurrent theory consistently interprets typical characteristics of regularmore » SS-OPV devices. Finally, these insights should encourage the design and OPV implementation of high-purity, high-mobility polymers, and other soft materials that have shown promise in organic field-effect transistor applications, but have not performed well in BHJ OPV devices, wherein they adopt less-than-ideal nanostructures when blended with electron-accepting materials.« less

Authors:

Ray, Biswajit ^[1]; Baradwaj, Aditya G. ^[2]; Khan, Mohammad Ryyan ^[1]; Boudouris, Bryan W. ^[2]; Alam, Muhammad Ashraful ^[1]

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+ Show Author Affiliations

1. School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907,
2. School of Chemical Engineering, Purdue University, West Lafayette, IN 47907

Publication Date:

Wed Aug 19 00:00:00 EDT 2015

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Re-Defining Photovoltaic Efficiency Through Molecule Scale Control (RPEMSC); Purdue Univ., West Lafayette, IN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1235144

Alternate Identifier(s):

OSTI ID: 1347977

Grant/Contract Number:  

SC0001085

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 112 Journal Issue: 36; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 14 SOLAR ENERGY; exciton; charge collection; organic photovoltaic; solar cell; organic defects