Light intensity dependence of organic solar cell operation and dominance switching between Shockley\u2013Read\u2013Hall and bimolecular recombination losses

Shinyoung Ryu,Soonil Lee,Ji-Yong Park,Na Young Ha,Y H Ahn

doi:10.1038/s41598-021-96222-w

Abstract

We investigated the variation of current density–voltage (J–V) characteristics of an organic solar cell (OSC) in the dark and at 9 different light intensities ranging from 0.01 to 1 sun of the AM1.5G spectrum. All three conventional parameters, short-circuit currents (Jsc), open-circuit voltage (Voc), and Fill factor (FF), representing OSC performance evolved systematically in response to light intensity increase. Unlike Jsc that showed quasi-linear monotonic increase, Voc and FF showed distinctive non-monotonic variations. To elucidate the origin of such variations, we performed extensive simulation studies including Shockley–Read–Hall (SRH) recombination losses. Simulation results were sensitive to defect densities, and simultaneous agreement to 10 measured J–V curves was possible only with the defect density of 5 times 10^{12} {text{ cm}}^{ - 3}. Based on analyses of simulation results, we were able to separate current losses into SRH- and bimolecular-recombination components and, moreover, identify that the competition between SRH- and bimolecular-loss currents were responsible for the aforementioned variations in Jsc, Voc, and FF. In particular, we verified that apparent demarcation in Voc, and FF variations, which seemed to appear at different light intensities, originated from the same mechanism of dominance switching between recombination losses.

Highlights

We investigated the variation of current density–voltage (J–V) characteristics of an organic solar cell (OSC) in the dark and at 9 different light intensities ranging from 0.01 to 1 sun of the AM1.5G spectrum
There is a non-monotonic variation in the “squareness” of the J–V curves, which we typically represent by fill factor (FF) p arameters[23]
In addition to the discrepancy between Voc and Fill factor (FF) variations, a quasi-linear Jsc increase in Fig. 2d indicates that qualitative arguments based on two recombination mechanisms are insufficient to manifest light-intensity dependence of the OSC operation

Summary

Introduction

We investigated the variation of current density–voltage (J–V) characteristics of an organic solar cell (OSC) in the dark and at 9 different light intensities ranging from 0.01 to 1 sun of the AM1.5G spectrum. Tracking light-intensity dependence of J–V characteristics is an efficient strategy to study essential mechanisms controlling OSC performance because variations in optical and electrical processes can occur simultaneously in response to light intensity c hanges[10,11,12,22]. Combined with systematic simulations that can reproduce a measured set of J–V curves, light intensity-dependent studies can be useful in identifying key processes that determine J–V characteristics and elucidating the origin of variations in OSC performance parameters. For device simulation corresponding to operation under various illumination conditions, we first simulated position- and wavelength-dependent exciton generation rates in an AL, which resulted from photon absorption This optical part of simulation was done by using a multilayer OSC structure together with pre-determined optical constants of each constituent layer[21]. We used a device simulator SCAPS for electrical part of simulation after

Methods

Results

Conclusion